- 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

Add `watch` utility to streamline reacting to store changes

Rename two arguments to make it, subjectively, easier to distinguish them at a glance.

Previously watched values that were objects or arrays were compared by
shallow equality if only one watcher was passed to `watch` but compared
by strict equality otherwise. Strict equality was supposed to be used in
both cases.

This is more conventional in our usage of Redux elsewhere in the app.

Attempt to fix issue where wrong code was sometimes deployed

This check was temporarily removed in the previous commit to test the
changes.

This commit fixes an issue with the client's Jenkins pipeline that could
cause code for a recent but not-the-latest commit to master to be deployed to QA,
but with the version number corresponding to the latest commit.

---

The client's Jenkins CI/CD build is split into three phases:

 1. Checkout source, build, lint and test
 2. Publish QA release
 3. Publish prod release

Each of these phases was executed in a separate `node` block. Each node
block defines a task and Jenkins allocates a workspace directory for
that task. Workspace directories are named after the project, branch and
concurrent build number (eg. `/data/jenkins/workspace/client_master@2`).

Each workspace directory is "locked" for use by one task at a
time, but workspace directories are re-used when not locked. New
workspace directories are allocated as needed when concurrent builds
happen and all existing directories for a given (project, branch) are
locked.

If there was only one active build of the client's "master" branch,
phases (2) and (3) would re-use the same workspace directory and
everything would work as expected. If however there was a concurrent build,
phase (2) could end up using a different workspace directory than phase (1):

 1. Build A starts phase 1 and uses workspace dir #1
 2. Build B starts phase 1 and uses workspace dir #2
 3. Build A finishes phase 1, freeing workspace #1
 4. Build A starts phase 2, using workspace #1
 5. Build A completes phase 2, freeing workspace #1
 6. Build B completes phase 1 and starts phase 2, using workspace #1

In step (6), build B runs phase 2 (the "Publish QA" step) using the
workspace created by build A and publishes the code checked out by build
A with the version number associated with build B.

The fact that this kind of screw-up is even possible shows a deeper
issue with our current CI setup. Nevertheless, this commit addresses the
immediate issue by:

 1. Putting phases (1) and (2) in the same `node` block so that they are
    guaranteed to use the same workspace directory. There was no benefit
    to making them separate tasks.

 2. Adding a `checkout scm` command at the start of phase (3) so that it
    will definitely deploy the same code that was tested and deployed to
    QA in steps (1) and (2)

[1] https://github.com/jenkinsci/pipeline-plugin/blob/master/TUTORIAL.md#understanding-syntax

Fix visibility of submenu item focus rings

Increase highlight opacity

Item submenus inside the `Menu` component are wrappd in a `Slider` to
enable an animated expand/collapse of the submenu. The `Slider` used
`overflow: hidden` to hide any content while collapsed or transitioning.
However this had the unintended effect of clipping focus rings which
extended beyond the bounds of the content.

Fix the issue by changing the `overflow` property to `visible` once the
slider's content is fully visible.

Add assert.rejects()

Replace assertPromiseIsRejected and toResult with assert.rejects
Signed-off-by: Kyle Keating <kkeating@hypothes.is>

- This is used to patch in helper methods into the global assert object such as `rejects()` for testing.
- The new rejects method gives tests the ability to easily test error results in async methods that return a promise.
- Replace all async try/catch tests with assert.rejects
Signed-off-by: Kyle Keating <kkeating@hypothes.is>

This will be used to streamline a common pattern in our code for
reacting to changes in state selected from the central Redux store.

The utility is a standalone function rather than a method of the store
so that it can easily be used with mock stores and also other data
sources in future.

```
watch(
  store.subscribe,
  () => store.getState().someValue,
  (currentValue, prevValue) => { /* Handle change */ },
);
```

Increase the opacity of highlights from 30% to 40% to improve the
visibility of highlights, especially on very light/white backgrounds. Following
https://github.com/hypothesis/client/pull/2017, we can do this without reducing
contrast of highlighted text in PDFs.

Only the color of "first level" (non-nested) highlights was increased,
as nested highlights already had the higher level of contrast.

Improve readability of PDF highlights

These highlights are used to enable various Hypothesis UI interactions
for annotated content on PDF pages which are not yet rendered. They
should be visually hidden however. The highlight in the text layer is hidden
by the `annotator-placeholder` CSS class. We also need to avoid creating
an SVG highlight.

Bump karma from 4.4.1 to 5.0.1

Bump core-js from 3.6.4 to 3.6.5

Bump autoprefixer from 9.7.5 to 9.7.6

Bump escape-string-regexp from 1.0.5 to 3.0.0

Bump sinon from 9.0.1 to 9.0.2

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.7.5 to 9.7.6.
- [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/9.7.5...9.7.6)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 17.1.4 to 17.2.1.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v17.1.4...v17.2.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.653.0 to 2.656.0.
- [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/v2.653.0...v2.656.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [jquery](https://github.com/jquery/jquery) from 3.4.1 to 3.5.0.
- [Release notes](https://github.com/jquery/jquery/releases)
- [Commits](https://github.com/jquery/jquery/compare/3.4.1...3.5.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [core-js](https://github.com/zloirock/core-js) from 3.6.4 to 3.6.5.
- [Release notes](https://github.com/zloirock/core-js/releases)
- [Changelog](https://github.com/zloirock/core-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zloirock/core-js/compare/v3.6.4...v3.6.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/preset-env](https://github.com/babel/babel) from 7.9.0 to 7.9.5.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.9.0...v7.9.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump terser from 4.6.10 to 4.6.11