Fix the `ctaBackgroundColor` theme property not being applied properly
to the drop-down arrow on the right-hand side of the "Post to <group>"
button.

Fix an incorrect call to `applyTheme` which passed an invalid theme
property name. This is a regression from when this component was converted
from AngularJS to Preact in 7bbb8a60.

Also improve the type definitions of `applyTheme` and add a test to help catch
such mistakes in future.

Fixes #2439

- share-annotations-panel
- sidebar-content-error
- sidebar-content
- stream-content

- annotation-share-info
- annotation-viewer-content
- annotation.js

Make it easier to explore all the code and resources that make up the
development server by putting them all in one directory.

Replace the index page of the dev server with a more useful landing
page. The iframe has been removed because it is something we're not
testing most of the time and there are remaining issues with the way
multiple frames are supported in the sidebar. A separate test document
can be added for this purpose in future.

- annotation-user
- annotation-header
- filter-status

- thread-list
- thread-card
- thread
- timestamp

- help-panel
- stream-search-input
- toast-messages
- version-info

Bumps [wrap-text](https://github.com/IonicaBizau/wrap-text) from 1.0.8 to 1.0.9.
- [Release notes](https://github.com/IonicaBizau/wrap-text/releases)
- [Commits](https://github.com/IonicaBizau/wrap-text/compare/1.0.8...1.0.9)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Per PR feedback, be explicit about the kind of exception that occurred.

Fix a test that was failing but failing in a way that went unreported
previously due to a combination of it occurring after the test function returned
because of a missing `await` call and because of the issue with uncaught
exceptions between tests described in https://github.com/hypothesis/client/issues/2249.

This test was failing but the failure was only reported after the test
function returned due to a missing `await`.

Due to an issue with the interaction between mocha and karma-mocha [1],
uncaught exceptions or promise rejections that occur in between tests
can cause the test run to stop immediately yet incorrectly report that
all tests executed succesfully and hence CI runs / Jenkins builds
incorrectly report their status.

This commit works around the issue until the problem is resolved in
mocha / karma-mocha by adding an `afterEach` hook which will re-throw
any uncaught exceptions and ensure that mocha notices them and reports
the failure correctly to Karma.

[1] See comments on https://github.com/hypothesis/client/issues/2249

Bumps [mocha](https://github.com/mochajs/mocha) from 8.1.0 to 8.1.1.
- [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/v8.1.0...v8.1.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [whatwg-fetch](https://github.com/github/fetch) from 3.2.0 to 3.4.0.
- [Release notes](https://github.com/github/fetch/releases)
- [Commits](https://github.com/github/fetch/compare/v3.2.0...v3.4.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [preact](https://github.com/preactjs/preact) from 10.4.6 to 10.4.7.
- [Release notes](https://github.com/preactjs/preact/releases)
- [Commits](https://github.com/preactjs/preact/compare/10.4.6...10.4.7)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [axe-core](https://github.com/dequelabs/axe-core) from 4.0.0 to 4.0.1.
- [Release notes](https://github.com/dequelabs/axe-core/releases)
- [Changelog](https://github.com/dequelabs/axe-core/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/dequelabs/axe-core/compare/v4.0.0...v4.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint-plugin-mocha](https://github.com/lo1tuma/eslint-plugin-mocha) from 7.0.1 to 8.0.0.
- [Release notes](https://github.com/lo1tuma/eslint-plugin-mocha/releases)
- [Changelog](https://github.com/lo1tuma/eslint-plugin-mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/lo1tuma/eslint-plugin-mocha/compare/7.0.1...8.0.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [enzyme-adapter-preact-pure](https://github.com/preactjs/enzyme-adapter-preact-pure) from 2.2.1 to 2.2.2.
- [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/v2.2.1...v2.2.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.11.0 to 7.11.1.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/main/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.11.1/packages/babel-core)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.726.0 to 2.730.0.
- [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/v2.726.0...v2.730.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

group-list-item.js
group-list-section.js
group-list.js

Typechecking now completes for enough of the `src/` directory that we
can enable checking for all .js files except for tests and a small
number of files in `src/sidebar.

CoffeeScript imports are marked as expected errors for the moment. They
will be checked once those files are converted.

Flipgrid fixed an issue on their end that required us to make the iframe
for Flipgrid embeds taller than the actual content. This commit removes
the custom aspect ratio so that these videos will use the 16:9 default.

Tested by pasting this link into an annotation: https://flipgrid.com/s/030475b8ceff

Slack thread: https://hypothes-is.slack.com/archives/C1M8NH76X/p1596723935386100

`clearSelection` does the same thing

Typecheck the class that reads metadata from HTML documents and attaches
it to annotations as the `annotation.document` property.

This resulted in a few minor corrections to the `DocumentMetadata` type
in `src/types/annotator.js`.

- new-note-btn.js
- search-status-bar.js
- selection-tabs.js
- annotation-action-bar.js
- annotation-quote.js

Fix an a11y issue reported by axe-core [1] by adding an aria-label
attribute to several links that did not have text content. These links
all have `title` attributes but axe v4.0.0 does not consider that a valid
label.

[1] https://dequeuniversity.com/rules/axe/4.0/link-name?application=axeAPI

Bumps [axe-core](https://github.com/dequelabs/axe-core) from 3.5.5 to 4.0.0.
- [Release notes](https://github.com/dequelabs/axe-core/releases)
- [Changelog](https://github.com/dequelabs/axe-core/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/dequelabs/axe-core/compare/v3.5.5...v4.0.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Add `src/types/pdfjs.js` module which defines the subset of the PDF.js
viewer API that the client actually uses and make use of it in
`src/annotator/anchoring/pdf.js` and `src/annotator/plugin/pdf-metadata.js`
to typecheck these files.

As well as helping to catch errors and JSDoc mistakes in these files,
this should also make future PDF.js upgrades easier because we can see
what PDF.js APIs the client actually relies on.

The `MenuItem` component never used this prop. It was passed by mistake
in `SortMenu` as a duplicate of the `label` prop.

Enable typechecking of most JS files in src/annotator except for:

 - The entrypoint index.js file. This cannot be usefully checked since
   it imports many CoffeeScript files
 - pdf-sidebar.js - This extends a class currently written in
   CoffeeScript
 - src/annotator/anchoring/pdf.js - This requires types for various
   PDF.js globals to be defined
 - The `annotator/plugin` directory