f96af43d added support for PDF.js >= v2.5.207 by changing an event
listener to use PDF.js's internal event bus rather than DOM events.
However there was another DOM event listener for the `pagesloaded` event
in `src/annotator/anchoring/pdf.js` that should also have been updated but was
overlooked. This didn't cause a problem in testing with the dev server because
the test documents load quickly enough that they are already loaded by the time
the client's anchoring logic ran.

This commit updates the way that the client listens for events from
PDF.js to use the event bus where available and only fall back to the
DOM in versions of PDF.js that don't support it.

 - Use PDF.js's event bus to listen for `documentload`/`documentloaded`
   and `pagesloaded` events

 - Add a fallback method to wait for event bus to become available in
   versions of PDF.js which support the eventBus but don't have the
   `initializedPromise` API

 - Improve the documentation around which versions of PDF.js support
   different event types and event dispatch methods

 - Add tests to cover the behavior from different releases of PDF.js

For an overview of the different versions of PDF.js that the client
needs to support, see https://github.com/hypothesis/client/issues/2643.

`TagEditor` tested if the browser was IE 11 to determine whether to
check the `inputType` property of `InputEvent`. However it is not only
IE 11 that did not support this property.

From reading the comments in https://github.com/hypothesis/client/pull/1558 it
appears that the `inputType` checks was originally added to resolve an
issue with accepting suggestions by pressing Enter in an earlier version
of `TagEditor` that used the `<datalist>` element. As far as I can tell
this is no longer applicable. `<datalist>` was replaced by a custom UI
and accepting suggestions by pressing Enter works without this logic.
Therefore this commit removes it entirely.

The sidebar application failed to load in Safari 10 due to the ES 2018
polyfill bundle, which contains a polyfill for
`Promise.prototype.finally`, not being loaded in that browser.

The issue was that 'es2018' was not listed in the polyfill bundles to
build in `gulpfile.js` or in the list of bundles required by the sidebar
app in `boot.js`.

This commit fixes these issues and makes the issue less likely to occur
in future by:

 - Removing the need to manually list each polyfill bundle in
   `gulpfile.js`. Instead the `src/shared/polyfills` dir is listed and
   every non-`index.js` file is used as the root of a bundle.
 - Factoring out the polyfills common to the sidebar and annotator app
   into a variable and including "es2018" there

Element.closest is natively supported [1] by our minimum browser targets.

[1] https://developer.mozilla.org/en-US/docs/Web/API/Element/closest#Browser_compatibility

This API is available in Edge Legacy but with a quirk that arguments
that are optional in the spec are required in this browser.

This fixes an issue that the client would incorrectly abort startup in
Edge Legacy with a warning that the browser is unsupported.

This polyfilled the optional-ness of the `filter` and deprecated
`expandEntityRefrences` arguments of `document.createNodeIterator` in IE
11, which is no longer supported.

This was only needed for IE 11, which is no longer supported.

This was only needed for IE 11, which is no longer supported.

This was only needed for IE 11, which is no longer supported.

Run a series of feature tests at the very start of the boot process and
abort with a console warning if they fail.

We display a console warning rather than a louder warning to avoid being
disruptive on sites maintained by publishers which embed Hypothesis and
which still want to support older browsers. On those sites the
Hypothesis annotation feature will simply be missing.

The sidebar app failed to start in Edge Legacy due to `element.dir
= "auto` assignments causing an exception during Preact component
rendering. We already had a fix for this that applied to IE 11, so the
fix for this problem is to change the check to test for the bug
specifically rather than testing the user agent.

Bumps [sass](https://github.com/sass/dart-sass) from 1.26.12 to 1.27.0.
- [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/1.26.12...1.27.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [terser](https://github.com/terser/terser) from 5.3.4 to 5.3.5.
- [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/v5.3.4...v5.3.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 5.25.0 to 5.26.0.
- [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/5.25.0...5.26.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [focus-visible](https://github.com/WICG/focus-visible) from 5.1.0 to 5.2.0.
- [Release notes](https://github.com/WICG/focus-visible/releases)
- [Commits](https://github.com/WICG/focus-visible/compare/v5.1.0...v5.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [sinon](https://github.com/sinonjs/sinon) from 9.1.0 to 9.2.0.
- [Release notes](https://github.com/sinonjs/sinon/releases)
- [Changelog](https://github.com/sinonjs/sinon/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sinonjs/sinon/compare/v9.1.0...v9.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.767.0 to 2.771.0.
- [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/v2.767.0...v2.771.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.21.3 to 7.21.4.
- [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/v7.21.3...v7.21.4)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint](https://github.com/eslint/eslint) from 7.10.0 to 7.11.0.
- [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/v7.10.0...v7.11.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Code reorganisation:

* Adder has a simplified API: added a public method display that internally calls private methods _target and _showAt
* Performance improvement in _target method by removing multiple calls to this._width() and this._height()
* More strict type for arrowDirection

resolves #2009

This makes it easier to use the dev server for testing Hypothesis on
mobile devices with smaller screens (ie. phones).

The issue is not specific to Chrome-based browsers on Android, although
it does cause much more of a problem in that browser than Safari on iOS.

Expand and revise several JSDoc comments following feedback from Lyza in
https://github.com/hypothesis/client/pull/2622.

Improves the documentation of parameter types and class and method
descriptions.

When selecting text on the android, it was possible to also highlight the text inside the buttons in the adder. When this happened, the range would grab everything from where you started to highlight to the very end of the dom because the adder is attached as the last node inside body.

The simple fix is to prohibit text selection inside the adder which prevents the selection from getting the adder itself.

Add a non-OCR'd PDF available to the local dev server to aid
developers

As one of the final parts of removing the client's jQuery dependency,
use DOM APIs to defer annotator initialization until the document has
loaded.

There is no CoffeeScript code left in the codebase so we don't need this
any more.

Make current set of tests pass

* Add tests for extracted code
* Skip a couple of `BucketBar` tests that are difficult to patch up
  during migration

Remove the logic that was intended to ignore Hypothesis UI when
generating range selectors.

We don't need this any more because all Hypothesis UI elements in the
host page which contain text have `user-select` set to prevent text
selection. This affects the bucket bar, vertical toolbar and adder.

In addition, the logic did not serve its intended purpose as it only applied to
range selector generation. If the user did somehow succeed in selecting text in
the bucket bar for example the client would still generate quote and position
selectors that referred to that content. What the client would need to
do instead is modify the range from which the annotation's selectors
were generated.

As a side effect this fixes a regression introduced in a5540581 which caused
range selector generation to fail in Chrome and Firefox due to use of
`:not(<inner selector>)` selector where `<inner selector>` is a
list of selectors (the `IGNORE_SELECTOR` value from `guest.js`).

The recently-added `button-hover` mixin, used by the base `button`
mixin and thus inherited by other button mixins, applied hover styling
to focused buttons, but other button mixins that adjust hover styling
were not applying hover styling to focused buttons.

Update mixins to consistently apply hovered styling to focused buttons

Fixes #2610

Handle scenarios flagged by type checking where `nodeFromXPath` may
return `null` or a non-Element node. Previously it could never return
`null` but would throw an exception if the node was not found. In the
new code a check is needed.

The case where `nodeFromXPath` returned a non-Element node would never
happen with XPaths generated by the client but could happen if an
annotation was created via the API with a non-simple XPath.