Convert the `Delegator` base class to JS and rewrite the documentation
to match current functionality and usage. Also simplify the `options`
initialization and add a note about why the constructor reads
`this.options` before assigning it.

I tried to convert the `Plugin` class as well but encountered an issue
with interaction between Babel-compiled derived classes and CoffeeScript
sub-classes (in particular, the `BucketBar` class), so it looks like
`Plugin` sub-classes will need to be converted first.

Consolidate annotation-editing logic and sub-components within
`AnnotationEditor`. `AnnotationBody` is for rendering content, and
`Annotation` is relieved of managing editing-related callbacks.

These changes also add a new feature: When saving an annotation,
`AnnotationEditor` will check the contents of `TagEditor`'s input
element. If any text remains there that has not yet bet "committed"
as a tag, that text will be added as a tag. This is to prevent tags
accidentally getting "lost" on save.

Fixes https://github.com/hypothesis/product-backlog/issues/1122

This component will take over the editing-related responsibilities from
`AnnotationBody` and `Annotation`

This selector is not referenced anywhere else in the code.

 - Fold `highlightsAt` into `annotationsAt` as it is only used in one
   place

 - Rename `xor` variable to a more obvious name

The `Delegator` events system was used for handling two kinds of event:

 - DOM events on highights and document elements
 - Custom events internal to the "annotator" module

The handling of DOM events has been moved into the `Guest` class, so
`Delegator` is now used only to subscribe to and publish internal
events. This commit removes the DOM event handling code.

There is an existing issue, noted in this commit, that the `destroy`
method only removed event handlers declared via the `events` property
and not those added later by `subscribe`.

This removes the last remaining usage of the `events` property of
`Delegator`, enabling that code to be removed.

The way that the `Guest` class listened to clicks on highlights and the
document involved a DOM event-listening abstraction in `Delegator` that
is no longer used for anything else in the code. This indirection made
it more complicated to follow how these events were handled.

This commit replaces the event handling for clicks, hovers and taps on
highlights and the page with regular DOM event listeners in the `Guest`
class.

Bumps [whatwg-fetch](https://github.com/github/fetch) from 3.4.0 to 3.4.1.
- [Release notes](https://github.com/github/fetch/releases)
- [Commits](https://github.com/github/fetch/compare/v3.4.0...v3.4.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [karma](https://github.com/karma-runner/karma) from 5.1.1 to 5.2.1.
- [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/v5.1.1...v5.2.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 5.21.4 to 5.22.3.
- [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/5.21.4...5.22.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [terser](https://github.com/terser/terser) from 5.2.1 to 5.3.0.
- [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/v5.2.1...v5.3.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [js-polyfills](https://github.com/inexorabletash/polyfill) from 0.1.42 to 0.1.43.
- [Release notes](https://github.com/inexorabletash/polyfill/releases)
- [Commits](https://github.com/inexorabletash/polyfill/compare/v0.1.42...v0.1.43)
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Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.0.4 to 18.0.5.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.0.4...v18.0.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.0.14 to 2.0.15.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/2.0.14...2.0.15)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint](https://github.com/eslint/eslint) from 7.8.0 to 7.8.1.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v7.8.0...v7.8.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.743.0 to 2.747.0.
- [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/v2.743.0...v2.747.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.11.5 to 7.11.6.
- [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/v7.11.6/packages/babel-core)
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It turns out that there is an implicit requirement that `Host` call its
parent constructor _after_ the `.annotator-frame` element has been
created and added to the DOM. This needs refactoring to avoid the hidden
dependency, but I'm leaving that for later to focus on the CoffeeScript
=> JS conversion here.

Rewrite the config param filtering to make it more obvious what is going
on and extract a couple of helper functions to make the test more
readable.

There was no good reason for it to be in the middle of the function.

This is a straightforward conversion with decaffeinate, followed by
manual fixups of lint errors etc.

Help user see what part of an entered tag is a match for a suggested tag

Change the matching logic for determining whether a given suggested tag
(`tag`) matches the currently-typed tag field text (`query`).

Formerly, `tag` would match `query` if `tag` were a substring of `query`
in any position. However, this creates a lot of noise in the matches and
is not commonly what folks are after.

Now, `tag` will match `query` if:

* `tag` starts with `query` OR
* `query` occurs within `tag` after a word boundary or a non-word
   character

Thus, a `query` of "app":

* Would match the `tag` "apple"
* Would match the `tag` "crab apple" ("app" occurs after a word boundary)
* Would match the `tag` "crab.apple" ("app" occurs after non-word char)
* Would NOT match the `tag` "crabapple"

- Refactor `range-js-test` and remove specific testing of internal functions such as `findChild` and `nodeFromXPathFallback`.

- `nodeFromXPath` ported code does not contain any code path for XML handling as the coffeescript previously did. This code was however previously untested and difficult to reproduce in practice. It was likely was never or rarely used and is over 6 years old.

Bumps [bl](https://github.com/rvagg/bl) from 4.0.2 to 4.0.3.
- [Release notes](https://github.com/rvagg/bl/releases)
- [Commits](https://github.com/rvagg/bl/compare/v4.0.2...v4.0.3)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [preact](https://github.com/preactjs/preact) from 10.4.7 to 10.4.8.
- [Release notes](https://github.com/preactjs/preact/releases)
- [Commits](https://github.com/preactjs/preact/compare/10.4.7...10.4.8)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [commander](https://github.com/tj/commander.js) from 6.0.0 to 6.1.0.
- [Release notes](https://github.com/tj/commander.js/releases)
- [Changelog](https://github.com/tj/commander.js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/tj/commander.js/compare/v6.0.0...v6.1.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [mocha](https://github.com/mochajs/mocha) from 8.1.1 to 8.1.3.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mochajs/mocha/compare/v8.1.1...v8.1.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

For features going forward, nest in a single `experimental` object so
that `experimental` features can be white-flagged in one go in, e.g.,
via

- Don't close sidebar on click if the click is on highlighted annotation
  text. Fixes a judder (Fixes #2372)
- Don't close sidebar on click if `closeSidebarOnDocumentClick` is
  falsey (for side-by-side support)

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.739.0 to 2.743.0.
- [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/v2.739.0...v2.743.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint](https://github.com/eslint/eslint) from 7.7.0 to 7.8.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v7.7.0...v7.8.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [prettier](https://github.com/prettier/prettier) from 2.1.0 to 2.1.1.
- [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/2.1.0...2.1.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.0.3 to 18.0.4.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.0.3...v18.0.4)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.0.12 to 2.0.14.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/2.0.12...2.0.14)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>