This enables testing handling of the client's discovery of existing
frames (on page load) as well as handling of dynamic addition and removal after
the client has started.

Use separate channels for sending messages to guests vs the host in the
sidebar, even for the common case when there is only one guest and it is
the same frame as the host.

This change makes it clear for readers which part of the annotator code
is intended to handle a particular message from the sidebar. It is also
a step towards supporting host frames that are not guests. This will be
needed in ebook readers where the host frame provides the navigation UI
and contains the frame displaying the book content, but should not be
annotatble itself.

 - Remove the `bridge` service in the sidebar. The `frameSync` service
   now provides the entry point for other services/components to make RPC calls
   to the host or guest frames. Currently the only use case is
   sending notifications to the host via `FrameSyncService.notifyHost`.

 - Create separate `Bridge` instances in `FrameSyncService` for sidebar
   <-> guest and sidebar <-> host communication. The sidebar <-> guest
   bridge works the same as before. The sidebar <-> host bridge
   is established by having `FrameSyncService` create a MessageChannel
   when sending the `hypothesisSidebarReady` notification to the host.

   The sidebar / host frames then add respective ports of this channel
   to a Bridge instance.

 - Change the various existing RPC calls between frames to use either
   the guest <-> sidebar or host <-> sidebar communication channels as
   appropriate

Show the URLs of all frames connected to the sidebar in the Version info
tab of the Help panel. Previously only the URL of the main frame was
shown.

Initially this will mainly be useful for client developers to check that
the expected set of frames are connected to the sidebar in different
scenarios.

`Annotator` is not a great name for this interface, but at least make
the link between it and Guest clearer by improving its documentation and
marking Guest as explicitly implementing it.

This adds a new integration for the VitalSource Bookshelf reader. It is
comprised of two separate sub-integrations, one for the "container"
frame into which the client is initially loaded, and a separate one for
the "content" frame that displays the book content.

The container frame integration is responsible for injecting the client
into the content frame and re-injecting after a navigation. All the
annotation-related functionality is a no-op in this frame. The logic for
injecting the client depends on a stub method in the Guest class which
will be implemented separately.

The content frame integration mostly delegates to the HTML integration,
but it customizes the document metadata saved with annotations and also
prevents the VitalSource viewer's native selection controls from
interfering with Hypothesis's ones.

All frontend Hypothesis app are going to have the same base line as
this:

https://github.com/hypothesis/bouncer/pull/469/commits/6a01199bfc196a8932be271f61c07029dbf886c5

Add a `canAnnotate` method to the `Integration` interface to indicate
whether a range is part of the annotatable content of the document. This
allows integrations to signal whether the Annotate/Highlight toolbar
should be shown for a given selection.

Implement it for PDFs by returning `true` if the range is part of the
text layer of a single page. Implement it for HTML documents by always
returning true.

Fixes #3790

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.11.1 to 18.11.4.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.11.1...v18.11.4)

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Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.26.0 to 7.26.1.
- [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/v7.26.0...v7.26.1)

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Bumps [babel-plugin-mockable-imports](https://github.com/robertknight/babel-plugin-mockable-imports) from 1.7.1 to 1.8.0.
- [Release notes](https://github.com/robertknight/babel-plugin-mockable-imports/releases)
- [Changelog](https://github.com/robertknight/babel-plugin-mockable-imports/blob/master/CHANGELOG.md)
- [Commits](https://github.com/robertknight/babel-plugin-mockable-imports/compare/v1.7.1...v1.8.0)

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`globalThis` is the preferred way of accessing the global object
regardless of environment. It also works in eg. Rollup whereas `global`
does not.

This is in preparation for switching to an ES module-oriented bundler.

Bumps [@actions/core](https://github.com/actions/toolkit/tree/HEAD/packages/core) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/actions/toolkit/releases)
- [Changelog](https://github.com/actions/toolkit/blob/main/packages/core/RELEASES.md)
- [Commits](https://github.com/actions/toolkit/commits/HEAD/packages/core)

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Bumps [@hypothesis/frontend-shared](https://github.com/hypothesis/frontend-shared) from 3.11.0 to 3.12.0.
- [Release notes](https://github.com/hypothesis/frontend-shared/releases)
- [Changelog](https://github.com/hypothesis/frontend-shared/blob/main/CHANGELOG.md)
- [Commits](https://github.com/hypothesis/frontend-shared/compare/v3.11.0...v3.12.0)

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Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.995.0 to 2.999.0.
- [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/v2.995.0...v2.999.0)

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Although the `delay` utility function is a small function that can
almost be in-lined, I decided to create a common `delay` function in
`wait.js` and replace all usage in tests by the new function.

This adds a mock version of the VitalSource Bookshelf reader to the dev
server. It includes only the essential aspects of the viewer's structure that
will trigger VitalSource-specific functionality.

The Guest implementation no longer has any logic which is specific to a
particular document type (PDF, HTML etc.). These details are now all
handled by the Integration implementation returned by
`createIntegration`.

This commit refactors the Guest tests to use a single Integration fake
instead of using different fakes to simulate HTML and PDF documents.

Move the logic for determining which document type/viewer integration to
create out of the annotator entry point and Guest and into a
`createIntegration` factory method in annotator/integrations/index.js

This reduces the number of places that need to change when we add new
integrations, and puts the logic for determining whether a particular
integration can be used in the current environment alongside the
corresponding implementation.

Because of the sometimes-arcane nature of grid layouts, it is sometimes
necessary to apply definite width values on grid areas (versus `auto`)
to prevent content from escaping.

This fixes a situation in which very long unbroken quoted excerpts could
blow out the column width in the Notebook.

See https://css-tricks.com/preventing-a-grid-blowout/

This was created to simulate a scenario in VitalSource's book reader,
but they changed their reader so that it no longer uses a tall frame.

This is a prerequisite for moving to a modern ES-module oriented module
bundler such as Rollup.

There is one remaining import ('preact/debug') which was not converted
because that is conditional, and top-level `import` statements can't be
conditional. That might need to use either `import(...)` or a different
approach.

This required adapting pattern library import paths due to changes in
https://github.com/hypothesis/frontend-shared/pull/200.

Remove logic that is no longer required with the current Hypothesis
client and PDF.js version.

See https://github.com/hypothesis/browser-extension/pull/658.

`String.protoype.substr` is a deprecated method (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr). It is recommended to be replaced by `String.prototype.substring` method (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring).

The pattern library no longer serves by default at `/ui-playground`, so
we need to set a `baseURL`.

Bumps [mocha](https://github.com/mochajs/mocha) from 9.1.1 to 9.1.2.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mochajs/mocha/compare/v9.1.1...v9.1.2)

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Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 6.12.0 to 6.13.2.
- [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/6.12.0...6.13.2)

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Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 10.3.4 to 10.3.6.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/compare/10.3.4...10.3.6)

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Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.3.2 to 2.3.3.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/2.3.2...2.3.3)

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Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.991.0 to 2.995.0.
- [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/v2.991.0...v2.995.0)

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Bumps [terser](https://github.com/terser/terser) from 5.8.0 to 5.9.0.
- [Release notes](https://github.com/terser/terser/releases)
- [Changelog](https://github.com/terser/terser/blob/master/CHANGELOG.md)
- [Commits](https://github.com/terser/terser/compare/v5.8.0...v5.9.0)

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Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.10.0 to 18.11.1.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.10.0...v18.11.1)

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