- Introduce a union type for current route names

 - Use `Record<Key, Value>` rather than `Object.<Key, Value>` as it is
   stricter (eg. it is non-nullable)

Services in `src/sidebar/services` are effectively classes. They are
currently implemented with a convention that was more common pre-ES6 where
the constructor is a function that creates the fields as local variables
and the methods using closures and returns an object that references the
closures.

This pattern has advantages, especially pre-ES6, as it avoids issues with
incorrect use of `this` and hides internal state from consumers. However
it also has downsides:

 - It is less obvious to readers that they are looking at something that
   is logically a class

 - This is not an idiom we use elsewhere in the codebase, where we use
   native classes instead

 - Static analysis tools don't support this pattern for creating a class
   as well as they support a native class. For example `TS` creates a
   named type for native classes, which is convenient to reference
   in JSDoc comments

This commit starts a process of refactoring service classes to ES
classes which are named `<Thing>Service`, using the router service as a
first example. Per recently agreed conventions, the classes are named
rather than default exports.

When the host config value for `requestConfigFromFrame` is an object containing a string and a number, it is assumed that the remaining host config is be fetched from the parent frame via RPC. In this context, any other values passed along via the iframe URL hash are ignored. One such value is the `group` which is used by the notebook to focus a group and filter only to that groups annotations.

This changes the method that merges the configs to allow that `group` value to be taken from the iframe's url and incorporated into the final merged config so that the notebook can set that value in its own store.

Both `SearchClient` and `load-annotations::load` had the same default
parameters. We have decided to leave the default parameters only in one
place instead of two.

This more specific test proves that removing the default parameters in
`load-annoationas::load` still uses the default parameters in the
`SearchClient`.

I added more specific types to services, that was otherwise listed as
`Object`.

This PR displays a button when there are new/deleted/updated annotations
on that the group. Clicking on the button updates the annotation thread
with the updated annotations. Currently, the button is placed by the
thread count.

If there are filters applied in the notebook the button is not shown.

To test this change make sure you update `h` to the latest version (so
it includes https://github.com/hypothesis/h/pull/6580)

This addresses PR feedback.

The visible part of PDF highlights are created by SVG elements which are
multiply-blended with the PDF content to enhance legibility of
highlighted text.  The blueish background for focused highlights was
still being applied to the transparent text layer on top of the PDF
which contains the `<hypothesis-highlight>` elements. This impacted the
legibility of focused highlights.

Improve the readability of PDF highlights by instead modifying the fill
color of the SVG element.

Bumps [@babel/preset-env](https://github.com/babel/babel/tree/HEAD/packages/babel-preset-env) from 7.13.12 to 7.13.15.
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- [Commits](https://github.com/babel/babel/commits/v7.13.15/packages/babel-preset-env)
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Bumps [core-js](https://github.com/zloirock/core-js/tree/HEAD/packages/core-js) from 3.10.0 to 3.10.1.
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- [Changelog](https://github.com/zloirock/core-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zloirock/core-js/commits/v3.10.1/packages/core-js)
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Bumps [postcss](https://github.com/postcss/postcss) from 8.2.9 to 8.2.10.
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- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.2.9...8.2.10)
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Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.13.14 to 7.13.15.
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- [Changelog](https://github.com/babel/babel/blob/main/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.13.15/packages/babel-core)
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Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.23.1 to 7.23.2.
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- [Changelog](https://github.com/yannickcr/eslint-plugin-react/blob/master/CHANGELOG.md)
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Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.880.0 to 2.884.0.
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- [Changelog](https://github.com/aws/aws-sdk-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js/compare/v2.880.0...v2.884.0)
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Bumps [typescript](https://github.com/Microsoft/TypeScript) from 4.2.3 to 4.2.4.
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- [Commits](https://github.com/Microsoft/TypeScript/compare/v4.2.3...v4.2.4)
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Bumps [enzyme-adapter-preact-pure](https://github.com/preactjs/enzyme-adapter-preact-pure) from 3.0.0 to 3.1.0.
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Bumps [katex](https://github.com/KaTeX/KaTeX) from 0.13.0 to 0.13.2.
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Bumps [eslint](https://github.com/eslint/eslint) from 7.23.0 to 7.24.0.
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- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
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In issue discussions, tests and various parts of the code there are
mentions of side-by-side mode being active or not. The `Guest` class
didn't store this state directly but instead had a
`closeSidebarOnDocumentClick` state which is always the inverse of
"is side-by-side active?".

Make the code easier to follow by storing the "is side-by-side active?" state
directly. This will also avoid a misnamed variable if in future the
state has other effects besides changing whether clicking on the
document closes the sidebar.

 - Replace `closeSidebarOnDocumentClick` with a private
   `_sideBySideActive` property, exposed via a read-only
   `sideBySideActive` getter

 - Refactor tests to only use the public API of Guest (calling
   `Guest#fitSideBySide` or reading `sideBySideActive`)

Remove the fallback logic that uses `location.href` and `document.title`
as the document URL and metadata if using the integration-specific code
(HTML or PDF) to get the document URL and metadata fails. Instead just
let the async exception propagate.  Currently this will result in no
annotation/highlight being created and a console error. In future we
should improve this by showing an error notification to the user.

Recording the wrong document metadata with an annotation is worse than
not creating an annotation at all: The user will be unaware that there
is a problem yet the annotation will likely fail to show up in future or
be displayed with completely wrong metadata in the Notebook. Therefore
we want the failure here to be obvious so that the user notifies us of
the problem and doesn't create a bunch of annotations which later
"disappear".

Fixes #3204

Add test to check that anchors not associated with the removed
annotation are preserved.

Rewrite the `Guest#anchor` method to simplify the control flow and
generally make it easier to understand and change. There are no
functional changes for annotations with zero or one entry in the
`target` field (all existing Hypothesis annotations).

There is a functional change to handling of annotations with multiple
targets. Previously `anchor` would try to be smart about only
re-anchoring targets which were not already anchored. In the new
implementation all targets for an annotation are re-anchored. This will have
no effect in practice because the Hypothesis client only supports
creating annotations with a single target and the h backend can only
store a single target per annotation. However the Hypothesis API does
allow for multiple targets per annotation, in line with the W3C Web
Annotations specs in which a single annotation can refer to multiple
parts of a document.

 - Convert `anchor` method to async and replace Promise chains with async/await

 - Replace the logic that removes existing anchors and highlights for an
   annotation with a call to the `detach` method. This required adding
   an internal parameter to `detach` to control whether `anchorsChanged`
   is emitted, so that `anchor` only emits `anchorsChanged` once.

 - Add an explicit error to `Promise.reject` calls in tests so that the
   tests are easier to debug if they fail

Devise a way to "extend" a common base playground app with local-app
routes and patterns

In the soon-future, we'll want to extract the common bits of the
UI Playground app to the `frontend-shared` repository. This is step 1.

Only `@forward` specific mixins and create a function to retrieve
color settings out of the `_config` partial

If opening the login popup window using `window.open` fails or succeeds
but fails to return a `Window` reference to the caller then show a more
helpful error message.

There are various rare scenarios (browser bugs, browser extensions)
which might cause this to happen. There is not a whole lot we can do to
recover, but at least we can show a better error message.

Use `IconButton` in `ShareAnnotationsPanel` and
`AnnotationShareControl`, with custom styling to make
the buttons pair well with a text input.

It would be ideal to create a design pattern from the
combo of the input + button in the future.

Replace uses of `Button` in the Thread component and adjust
styling for stronger alignment in both desktop and touch interfaces.