Enable typechecking for the following directories:

 - src/annotator/config
 - src/annotator/util
 - src/sidebar (excluding `ga.js`, `icons.js` and `index.js`)

Many functions in these directories are still not annotated, but this
will be added over time. `ga.js` was excluded because it deals with
globals added by Google Analytics. `icons.js` was excluded because TS
doesn't know how to handle `require('.../some-icon.svg')`. `index.js`
was excluded because that imports (and thus triggers checking for) every
other file in the sidebar app. It will need to be enabled last.

Don’t hide the component when `store.isLoading()` is true. This only causes a re-render of that component and momentarily removes it from the DOM. Its not actually invalid to show the filter buttons while loading because the filter is still being applied.

Extract styles from Annotation Body, License and Quote

Add utility classes for one-liners

Upgrade to ESLint v7.x

Update eslint-config-hypothesis which was in turn holding back various
other ESLint packages.

The newest update to eslint-plugin-react-hooks found an incorrect usage
of `useCallback` in `ThreadCard` where `debounce` was being called on
ever render instead of only when certain dependencies changed.

Add additional atomic mixins, variables

Enable typechecking for src/boot

Do additional consolidation with mixins and remove unused CSS

Adjust highlight icon styling for better visibility

Enable typechecking for `src/shared/*.js`

This mainly involved documenting the `config` option that is passed
around various functions in `src/boot/boot.js`.

Begin to add JSDoc types for client configuration objects

Enable typechecking of annotated functions in src/shared/, excluding
subdirectories for the moment.

This found a few minor mistakes with existing JSDoc usage.

The client's "sidebar" and "annotator" applications query configuration
from various sources (the host page, the H backend / browser extension
build, added dynamically by the app).

This commit begins the process of adding a centralized place to document
the types of these configuration objects and making typechecked modules
in `src/sidebar/util` use them.

- Make it a bit bigger so you can tell what it is
- Adjust baseline via margin to align it better with other row items

Add command to typecheck code and enable it for src/sidebar/util/

 - Ignore an unused function
 - Use a more modern idiom for setting the default value for a test
   seam

Reading the code it appeared that `getBreakpoint` could return `null`,
but this was not actually the case because the last item in
`BREAKPOINTS` always matches.

Revise the way `getBreakpoint` works to make it more obvious that it
will always return a breakpoint.

Bumps [eslint-plugin-jsx-a11y](https://github.com/evcohen/eslint-plugin-jsx-a11y) from 6.2.3 to 6.3.1.
- [Release notes](https://github.com/evcohen/eslint-plugin-jsx-a11y/releases)
- [Changelog](https://github.com/jsx-eslint/eslint-plugin-jsx-a11y/blob/master/CHANGELOG.md)
- [Commits](https://github.com/evcohen/eslint-plugin-jsx-a11y/compare/v6.2.3...v6.3.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Bumps [fetch-mock](https://github.com/wheresrhys/fetch-mock) from 9.10.1 to 9.10.2.
- [Release notes](https://github.com/wheresrhys/fetch-mock/releases)
- [Commits](https://github.com/wheresrhys/fetch-mock/compare/v9.10.1...v9.10.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Bumps [terser](https://github.com/terser/terser) from 4.7.0 to 4.8.0.
- [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/v4.7.0...v4.8.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Bumps [axe-core](https://github.com/dequelabs/axe-core) from 3.5.4 to 3.5.5.
- [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/v3.5.4...v3.5.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Bumps [sass](https://github.com/sass/dart-sass) from 1.26.8 to 1.26.9.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sass/dart-sass/compare/1.26.8...1.26.9)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.8.0 to 9.8.2.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/compare/9.8.0...9.8.2)
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- Single-line style rule can be replaced with a utility class