Use the `preserveScrollPosition` utility that was created for HTML / EPUB
side-by-side mode to preserve scroll position when side-by-side mode is toggled
in VitalSource PDFs.

 - Add a way to synchronously update the hidden text layer in VS PDFs

 - Wrap image size updates in VS PDFs in `preserveScrollPosition`

VitalSource PDF books currently create very tall iframes. When a user
scrolls through a PDF page, they are scrolling the _parent_ frame rather
than the iframe itself. The bucket bar and scrolling logic in the client
don't support this. The result is that:

 - Bucket bar buckets are in the wrong location and don't scroll as the
   user scrolls the parent frame
 - Clicking on an annotation / bucket tries to scroll only the iframe,
   not the parent frame.

To resolve this we need to do at least one of:

1. Support these tall iframes in the client generally
2. Forcibly change the height of the iframe and enable the iframe to scroll
3. Persuade VitalSource to change the iframe layout so that the content frame
   scrolls, rather than the parent frame. They previously did this for EPUBs
   already.

This commit implements a version of (2). If VS later apply (3) then we can
remove this workaround.

Add missing types found while trying to typecheck src/annotator with
`noImplicitAny` enabled.

 - Use "contains" rather than "returns" to describe tests of objects or
   object properties

 - Avoid deeply nested `describe` blocks that only contain a single test. This
   is just a preference not to have too many levels of nesting unless
   there are tests that benefit from grouping.

 - Revise description of tests for link properties (`link`,
   `documentFingerprint`, `favicon`) since these cover properties other
   than just `link`.

I have created a few additional `describe` sub-sections and re-grouped
tests by the resulting metadata property. This allow for a more atomic
testing.

Many classic texts that are freely available in VitalSource use `<div
class="para">` elements for paragraphs of text, instead of `<p>` elements.
Modify the logic for finding the main content of an HTML document to consider
these. We will probably want to make these selectors a configurable argument to
`guessMainContentArea` in future. Since there are only two of them and it is
unlikely to have ill effects outside of VitalSource books, I made it a general
feature of the HTML side-by-side mode implementation.

Fix an issue where the client failed to inject into some VitalSource book
chapters, by revising the tests used to decide whether a content frame should
have the client injected into it. The previous logic worked for most EPUBs and
PDF books, but failed for:

 - EPUB chapters which had no paragraph content (eg. only an image,
   table or list)

 - "Great Book" format EPUBs, which are used for many of the free
   classic texts available in VitalSource. These use `<div
   class="para">` elements for paragraphs instead of `<p>` elements
   (sigh).

Add a couple of test HTML documents in the local dev server that
demonstrate how the client renders in situations where the host page's
root font size is set tiny (10px) or huge (24px).

These test pages will help with solving
https://github.com/hypothesis/client/issues/4248

Add a README to the `styles` directory to help avoid confusion during
transition from SASS -> Tailwind.

Bumps [@sentry/cli](https://github.com/getsentry/sentry-cli) from 1.72.2 to 1.73.0.
- [Release notes](https://github.com/getsentry/sentry-cli/releases)
- [Changelog](https://github.com/getsentry/sentry-cli/blob/master/CHANGELOG.md)
- [Commits](https://github.com/getsentry/sentry-cli/compare/1.72.2...1.73.0)

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Bumps [rollup](https://github.com/rollup/rollup) from 2.67.3 to 2.68.0.
- [Release notes](https://github.com/rollup/rollup/releases)
- [Changelog](https://github.com/rollup/rollup/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rollup/rollup/compare/v2.67.3...v2.68.0)

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Bumps [@rollup/plugin-commonjs](https://github.com/rollup/plugins/tree/HEAD/packages/commonjs) from 21.0.1 to 21.0.2.
- [Release notes](https://github.com/rollup/plugins/releases)
- [Changelog](https://github.com/rollup/plugins/blob/master/packages/commonjs/CHANGELOG.md)
- [Commits](https://github.com/rollup/plugins/commits/commonjs-v21.0.2/packages/commonjs)

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Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.1077.0 to 2.1082.0.
- [Release notes](https://github.com/aws/aws-sdk-js/releases)
- [Changelog](https://github.com/aws/aws-sdk-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js/compare/v2.1077.0...v2.1082.0)

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Bumps [@rollup/plugin-virtual](https://github.com/rollup/plugins/tree/HEAD/packages/virtual) from 2.0.3 to 2.1.0.
- [Release notes](https://github.com/rollup/plugins/releases)
- [Changelog](https://github.com/rollup/plugins/blob/master/packages/virtual/CHANGELOG.md)
- [Commits](https://github.com/rollup/plugins/commits/run-v2.1.0/packages/virtual)

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  dependency-type: direct:development
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Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 6.17.9 to 6.18.0.
- [Release notes](https://github.com/getsentry/sentry-javascript/releases)
- [Changelog](https://github.com/getsentry/sentry-javascript/blob/master/CHANGELOG.md)
- [Commits](https://github.com/getsentry/sentry-javascript/compare/6.17.9...6.18.0)

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Bumps [enzyme-adapter-preact-pure](https://github.com/preactjs/enzyme-adapter-preact-pure) from 3.3.0 to 3.4.0.
- [Release notes](https://github.com/preactjs/enzyme-adapter-preact-pure/releases)
- [Changelog](https://github.com/preactjs/enzyme-adapter-preact-pure/blob/master/CHANGELOG.md)
- [Commits](https://github.com/preactjs/enzyme-adapter-preact-pure/compare/v3.3.0...v3.4.0)

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  dependency-type: direct:development
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Bumps [sass](https://github.com/sass/dart-sass) from 1.49.8 to 1.49.9.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sass/dart-sass/compare/1.49.8...1.49.9)

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Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.28.0 to 7.29.2.
- [Release notes](https://github.com/yannickcr/eslint-plugin-react/releases)
- [Changelog](https://github.com/yannickcr/eslint-plugin-react/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yannickcr/eslint-plugin-react/compare/v7.28.0...v7.29.2)

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  dependency-type: direct:development
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Bumps [@rollup/plugin-babel](https://github.com/rollup/plugins/tree/HEAD/packages/babel) from 5.3.0 to 5.3.1.
- [Release notes](https://github.com/rollup/plugins/releases)
- [Changelog](https://github.com/rollup/plugins/blob/master/packages/babel/CHANGELOG.md)
- [Commits](https://github.com/rollup/plugins/commits/babel-v5.3.1/packages/babel)

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  dependency-type: direct:development
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Bumps [puppeteer](https://github.com/puppeteer/puppeteer) from 13.3.2 to 13.4.0.
- [Release notes](https://github.com/puppeteer/puppeteer/releases)
- [Changelog](https://github.com/puppeteer/puppeteer/blob/main/CHANGELOG.md)
- [Commits](https://github.com/puppeteer/puppeteer/compare/v13.3.2...v13.4.0)

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Bumps [eslint](https://github.com/eslint/eslint) from 8.9.0 to 8.10.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/main/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v8.9.0...v8.10.0)

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  update-type: version-update:semver-minor
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Bumps [@rollup/plugin-replace](https://github.com/rollup/plugins/tree/HEAD/packages/replace) from 3.1.0 to 4.0.0.
- [Release notes](https://github.com/rollup/plugins/releases)
- [Changelog](https://github.com/rollup/plugins/blob/master/packages/replace/CHANGELOG.md)
- [Commits](https://github.com/rollup/plugins/commits/url-v4.0.0/packages/replace)

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  update-type: version-update:semver-major
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Bumps [postcss](https://github.com/postcss/postcss) from 8.4.6 to 8.4.7.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.6...8.4.7)

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  dependency-type: direct:development
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Support side-by-side mode in PDF books by simply resizing the content of
the page. This is similar to how side-by-side mode works in PDFs.

The width of the page in the VS PDF demo has been increased so that it
better matches the actual VS viewer, and also so that it triggers the
heuristics in the Guest class for detecting an iframe that fills the
parent frame.

This allows the client to detect, in most supported browsers, changes in the
size and position of the PDF book image which don't affect the window
size. This will be needed to support side-by-side mode for VS PDF books.
It may also help if VS resizes the book image for any other reason.

For Safari < 13.4, we fall back to using window resize events.

Toggling side-by-side mode in a web page reflows the content. If the absolute
scroll position stays the same, the logical position in the document will change
and the user would have to scroll to find the content they were
previously reading.

To avoid this add logic which picks content in the viewport to use as a _scroll
anchor_, before the document is resized. After the document is resized, the
scroll position is changed so that the vertical position of the scroll anchor in
the viewport is the same as before. This keeps most of the content on screen.

The scroll anchor is currently chosen by picking the first _word_
(non-whitespace substring of a text node) which is visible in the viewport,
represented as a DOM Range. This fine-grained scroll anchor is chosen rather
than eg. just a DOM element, because long paragraphs may change in size
substantially relative to the viewport after resizing the document, so just
preserving the location of the paragraph element would not preserve the content
that is on screen.

 - Add `preserveScrollPosition` helper in html-side-by-side.js which
   picks a scroll anchor, invokes a callback and then restores the
   position of the scroll anchor.

 - Make the HTML integration use `preserveScrollPosition` to preserve
   the scroll position after activating and de-activating side-by-side
   mode

 - Add helper functions in src/annotator/util/geometry for comparing
   DOMRect objects

When computing the amount of free space between the right edge of the
main content and the edge of the sidebar, allow for the padding
allocated between the sidebar and the content. This fixes an issue where
the main content would touch the sidebar exactly instead of having a
margin between it and the content.

Also tweak the padding value slightly to be a multiple of the 4px grid
cell size used in the design system.

Add calls to `act` around proxy method calls that trigger store changes
which in turn schedule deferred updates within Preact components. This
should hopefully fix an issue with flakey tests due to updates being
flushed after the tests have finished executing.

This makes the VS EPUB test page more accurately reflect the real VitalSource
viewer. More importantly, it also triggers the heuristic that the Guest class
uses to decide whether to enable side-by-side mode for an iframed guest.

To make side-by-side mode work for VitalSource EPUB books, the guest in
the VS content iframe needs to invoke the integration's `fitSideBySide`
method. This is done in a generic way by making guests in iframes call
this method, but only if they know that the iframe fills the host frame.

In the VitalSource integration, enable the side-by-side mode in the
underlying HTML document integration.

Implement side-by-side mode for HTML documents, disabled by default by a
a `HTMLIntegration.sideBySideEnabled` feature flag.

For ease of testing, some helpers have been split into a separate
html-side-by-side.js module.

Rename these types:

* `MergedConfig` -> `SidebarSettings`
* `HostConfig` -> `ConfigFromHost`
* `SidebarConfig` -> `ConfigFromSidebar`

Also, update type usage to favor `SidebarSettings` in services and
components.

Remove support for retrieving host configuration from an unspecified
ancestor frame. This was used by the legacy LMS application and is no
longer needed.