Move margin between `ThreadCard`s to `ThreadList`

Fix overflow on Thread contents

Add `overflow:hidden` to `.thread__content` containers such that long
un-breaking words (e.g. URLs) don’t break the sidebar width on nested
replies.

Fixes https://github.com/hypothesis/support/issues/101

Add differentiating link styling to tutorial

Several new developers have in the past asked why we use virtualization
since it adds complexity to the thread list implementation. Add a note
to the `ThreadList` docs explaining why it is needed.

Move the bottom margin on thread cards from the root `<div>` rendered by
`ThreadCard` to the wrapper div that contains it rendered by
`ThreadList`.

Aside from making conceptual sense that the list component controls the
spacing of list items, this also fixes an issue where the thread list
would sometimes jump when scrolling. This happened because the height of
individual threads was computed by calling `getElementHeightWithMargins`
on the wrapper div, which only accounted for margins on the wrapper div,
not margins on descendants. Note that due to margin collapsing, the descendant
margins did not contribute to the `getBoundingClientRect()` of the
wrapper div.

This normalizes the key names for events from non-standard browsers like IE11

Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.0.8 to 2.0.9.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/2.0.8...2.0.9)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Fixes #2054

Remove `FRAME_CONNECTED` event

Bump preact from 10.4.0 to 10.4.1

Bump @sentry/browser from 5.15.4 to 5.15.5

Bumps [preact](https://github.com/preactjs/preact) from 10.4.0 to 10.4.1.
- [Release notes](https://github.com/preactjs/preact/releases)
- [Commits](https://github.com/preactjs/preact/compare/10.4.0...10.4.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump puppeteer from 3.0.0 to 3.0.1

Bump prettier from 2.0.4 to 2.0.5

Do not use `button` element in `Menu` label

Menu labels are already rendered within a `button` element, so they
may not contain a `button` themselves, or else invalid HTML structure

Migrate `ThreadList` to preact

- Disable scroll anchoring, as it interferes with `ThreadList` and the
  calculation of visual threads and can cause infinite render loops
- Make scroll position in `ThreadList` fuzzier (50 px precision) to
  reduce scroll-event-related re-renders
- Improve test structure in `ThreadList` for these changes and better
  coverage

- Replace ng-1 `thread-list` with preact `ThreadList`
  (renamed from `ThreadListOmega`)
- Remove SCSS (new `ThreadList` has no CSS)
- Remove `virtual-thread-list`

This component renders top-level threads as “cards” in sidebar

Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 5.15.4 to 5.15.5.
- [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/5.15.4...5.15.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [puppeteer](https://github.com/puppeteer/puppeteer) from 3.0.0 to 3.0.1.
- [Release notes](https://github.com/puppeteer/puppeteer/releases)
- [Commits](https://github.com/puppeteer/puppeteer/compare/v3.0.0...v3.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [prettier](https://github.com/prettier/prettier) from 2.0.4 to 2.0.5.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/master/CHANGELOG.md)
- [Commits](https://github.com/prettier/prettier/compare/2.0.4...2.0.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump fetch-mock from 9.3.1 to 9.4.0

Remove `id` attributes from SVG elements

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 17.2.1 to 17.5.1.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v17.2.1...v17.5.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump puppeteer from 2.1.1 to 3.0.0

Bumps [karma](https://github.com/karma-runner/karma) from 5.0.1 to 5.0.2.
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](https://github.com/karma-runner/karma/compare/v5.0.1...v5.0.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

* Revert escape-string-regexp  back to 1.0.5

This broke IE 11. See issue https://github.com/sindresorhus/escape-string-regexp/issues/18Signed-off-by: Kyle Keating <kkeating@hypothes.is>

* Fix es2018 polyfill so it does not break IE11

Promise is undefined in IE11.
Signed-off-by: Kyle Keating <kkeating@hypothes.is>

* Add user-agent shared util

Adds 2 helper methods:
- isIE11
- isMacOS
Signed-off-by: Kyle Keating <kkeating@hypothes.is>

* Fix IE11 keyboard events

- IE11 uses special names for arrow keys that are different than the standard key names.
- Fix handleOnInput in tag-editor for IE11
- use isMacOS in markdown-editor

* Add renderer-options.js module

This module holds any renderer options to globally fix browser quirks or any other unique customizations we wish to add.

The dir=“auto” causes an exception in IE11. ie11DomReassignments() will simply replace that attribute’s value with an empty value so it does not break.

* Add browser-compatiblity-utils module

Current only holds one method used to translate key names used by IE11 to standardized names that all components can assume. This removes the need for special cases in each component when listening to keyboard events.

* missing code cov

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.656.0 to 2.658.0.
- [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/v2.656.0...v2.658.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [puppeteer](https://github.com/puppeteer/puppeteer) from 2.1.1 to 3.0.0.
- [Release notes](https://github.com/puppeteer/puppeteer/releases)
- [Commits](https://github.com/puppeteer/puppeteer/compare/v2.1.1...v3.0.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [fetch-mock](https://github.com/wheresrhys/fetch-mock) from 9.3.1 to 9.4.0.
- [Release notes](https://github.com/wheresrhys/fetch-mock/releases)
- [Commits](https://github.com/wheresrhys/fetch-mock/compare/v9.3.1...v9.4.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

These cause validation errors when an icon is used more than once