Simplify code in `search-filter.js` in preparation for enabling
typechecking of `src/sidebar/services`.

 - Use a single regex to parse the `<time><unit>` expression rather than
   two expressions per time unit.

 - Replace the user of manual offsets to get the field value which is
   error prone.

 - Update JSDoc of various functions

 - Provide a fallback in case a tokenizing regex fails to match. I
   haven't verified that this fallback ever gets used, but it keeps both
   TS and the human reader happier

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)
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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)
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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)
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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)
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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)
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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

Standardize font mixins

Extract "molecule" compositions into reusable mixins

Log which tests have executed during CI runs

During CI runs, but not local development, log which individual tests
have executed. This may help with debugging https://github.com/hypothesis/client/issues/2249.

Add atomic mixins for borders, icons

Add basic layout mixins

Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.10.2 to 7.10.3.
- [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/v7.10.3/packages/babel-core)
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