Upgrade mockable-imports Babel plugin and remove unused mock

There was a bug in previous versions of the plugin that allowed unused
mocks in certain cases.

Fix bug where direct linked group is duplicated

Do not add the direct-linked group to featuredGroups if it is already
present. This happens when a group is direct-linked to but the group
is already scoped to the page so the direct-linked group shows up twice.

Bump postcss from 7.0.14 to 7.0.16

Bump jquery from 3.4.0 to 3.4.1

Bump eslint-plugin-react from 7.12.4 to 7.13.0

Bump @octokit/rest from 16.25.0 to 16.25.2

Bump babel-plugin-istanbul from 5.1.3 to 5.1.4

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.14 to 7.0.16.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/7.0.14...7.0.16)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [babel-plugin-istanbul](https://github.com/istanbuljs/babel-plugin-istanbul) from 5.1.3 to 5.1.4.
- [Release notes](https://github.com/istanbuljs/babel-plugin-istanbul/releases)
- [Changelog](https://github.com/istanbuljs/babel-plugin-istanbul/blob/master/CHANGELOG.md)
- [Commits](https://github.com/istanbuljs/babel-plugin-istanbul/compare/v5.1.3...v5.1.4)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 16.25.0 to 16.25.2.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v16.25.0...v16.25.2)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [jquery](https://github.com/jquery/jquery) from 3.4.0 to 3.4.1.
- [Release notes](https://github.com/jquery/jquery/releases)
- [Commits](https://github.com/jquery/jquery/compare/3.4.0...3.4.1)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.12.4 to 7.13.0.
- [Release notes](https://github.com/yannickcr/eslint-plugin-react/releases)
- [Changelog](https://github.com/yannickcr/eslint-plugin-react/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yannickcr/eslint-plugin-react/compare/v7.12.4...v7.13.0)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Upgrade Preact

This fixes an issue with `Fragment`s containing a conditionally-rendered
last child.

Convert mocking to mockable imports (4/4)

Fix GitHub release generation script

Git has two types of tags, lightweight tags and annotated tags. Only
annotated tags have a "tag date" associated with them. Recently it
appears that releases have been tagged with lightweight tags rather than
annotated tags, which the `generate-change-list.js` script did not
handle.

 - When fetching the last tag, use the commit date as a fallback for the
   tag date, and bail with an error if no date can be found

 - Link to the HTML rather than JSON representation of a PR in release
   notes

 - Fix a warning about use of deprecated GitHub API pagination methods
   by switching to the pagination APIs described at
   https://octokit.github.io/rest.js/#pagination

 - Support running the `generate-change-list.js` script as a CLI tool
   for debugging using `node generate-change-list.js <tag name>`

 - Skip Dependabot PRs in the change list, as these add a lot of noise.
   Generally readers are going to be interested in non-maintenance PRs.

Even though the linked issue no longer applies, this module is never
used outside the sidebar app so there is no concern with it having
sidebar app-specific dependencies.

These are no longer used as all mocking is now done via the `$imports`
export added to modules by the mockable-imports Babel plugin.

This speeds up the test run by a few seconds as it eliminates an extra
parsing of the source.

Convert mocking to mockable imports (3/4)

This enables mocking of the `anchoring/html` module in tests without having
to patch the `anchoring` property after the class is constructed.

Convert mocking to mockable-imports (2/4)

Convert remaining uses of proxyquire to babel-plugin-mockable-imports,
except for modules written in CoffeeScript, as the Babel plugin needs an
update to support the way groups of `<var> = require(<module>)`
statements get compiled.

Bump @babel/preset-env from 7.4.3 to 7.4.4

Bump scroll-into-view from 1.9.5 to 1.9.6

Bumps [@babel/preset-env](https://github.com/babel/babel) from 7.4.3 to 7.4.4.
- [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/v7.4.3...v7.4.4)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bump @babel/core from 7.4.3 to 7.4.4

Bump enzyme-adapter-preact-pure from 1.13.0 to 1.13.1

Bump babel-plugin-istanbul from 5.1.2 to 5.1.3

Merge pull request #1096 from hypothesis/dependabot/npm_and_yarn/babel-plugin-transform-async-to-promises-0.8.10

Bump babel-plugin-transform-async-to-promises from 0.8.9 to 0.8.10

Bumps [babel-plugin-istanbul](https://github.com/istanbuljs/babel-plugin-istanbul) from 5.1.2 to 5.1.3.
- [Release notes](https://github.com/istanbuljs/babel-plugin-istanbul/releases)
- [Changelog](https://github.com/istanbuljs/babel-plugin-istanbul/blob/master/CHANGELOG.md)
- [Commits](https://github.com/istanbuljs/babel-plugin-istanbul/compare/v5.1.2...v5.1.3)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Note that the exports of the `anchoring/html` module are captured when
the class is constructed, so cannot be mocked later via `$imports`.
Instead the created `Guest` object has to be monkey-patched.

Convert proxyquire mocking of several CoffeeScript modules.

Merge pull request #1098 from hypothesis/dependabot/npm_and_yarn/babel-plugin-mockable-imports-1.3.1

Bump babel-plugin-mockable-imports from 1.2.0 to 1.3.1

Bumps [babel-plugin-mockable-imports](https://github.com/robertknight/babel-plugin-mockable-imports) from 1.2.0 to 1.3.1.
- [Release notes](https://github.com/robertknight/babel-plugin-mockable-imports/releases)
- [Changelog](https://github.com/robertknight/babel-plugin-mockable-imports/blob/master/CHANGELOG.md)
- [Commits](https://github.com/robertknight/babel-plugin-mockable-imports/compare/v1.2.0...v1.3.1)
Signed-off-by: dependabot[bot] <support@dependabot.com>