Following on @robertknight
[suggestion](https://github.com/hypothesis/client/pull/3035#pullrequestreview-599668554)
I created a tiny utility to make easier to unregister event listeners.

Avoid the need to customize various inline styles of the
`<hypothesis-banner>` element by positioning it at the top of the DOM as
the first child of `document.body`. As a result it naturally pushes the
PDF.js UI down. The only change we need to make to PDF.js's UI is to adjust
the size of the `#outerContainer` element so that it does not overflow the
bottom of the viewport.

Aside from making styling simpler, making the banner's DOM position
better match its visual position may help with reading order for screen readers.
Related to this the banner is currently missing useful semantic
information for a11y purposes.

I also removed the banner resizing handling for the moment on the basis that it
isn't that important.

For consistency with the rest of the UI elements rendered by the
annotator code, move the warning banner at the top of the PDF into
shadow DOM. This is also another step towards not needing to load any
global CSS (eg. our CSS reset) into the host page.

 - Change the container element for the banner from `<div>` to
   `<hypothesis-banner>` to match other `<hypothesis-*>` UI container
   elements
 - Move the `WarningBanner` component into `components/WarningBanner.js`
   and rename the CSS classes to match

Add `open` prop to allow components to do their own state management
of a `Menu`'s open/closed state.

On touch devices every touch event should eventually result on a click
event, as explained
[here](https://developer.mozilla.org/en-US/docs/Web/API/Touch_events/Supporting_both_TouchEvent_and_MouseEvent#event_order).
However, this is not true for mobile Safari versions < 13 (2019).

Because we still rely on listening to touchstart events, we decided to
sandbox the shadow DOMs, by stopping the propagation of click and
touchstart at that level. This prevents the bubbling of these events
outside the shadow DOM and better isolates the pieces of the application
that should not interact with the host page.

This was never an issue because the parent elements are destroyed,
however for completeness is better to add it.

In addition, I modified the test so that all the elements created are
added to a single parent container who is deleted after each test.

When no `contentContainer` has been specified in Sidebar's config, avoid
setting it when calling the `BucketBar` constructor. This leaves the
responsibility of determining how to observe whole-document scrolling up
to the BucketBar.

During code review it was suggested that "content container" might be
confused to mean the content of the bucket bar.

In current usage of the `BucketBar` we only ever have a single scrollable
container to observe. Simplify the `BucketBar` API to pass in this element directly
rather than a selector and add associated tests.

Prop-types checks are now globally disabled because we're using JSDoc +
TS instead.

Bumps [elliptic](https://github.com/indutny/elliptic) from 6.5.3 to 6.5.4.
- [Release notes](https://github.com/indutny/elliptic/releases)
- [Commits](https://github.com/indutny/elliptic/compare/v6.5.3...v6.5.4)
Signed-off-by: dependabot[bot] <support@github.com>

Components no longer have a `propTypes` property.

We no longer set `propTypes` on components.

This enables checking by TypeScript

Prop-types checking has been replaced by JSDoc + TypeScript.

Prop-types checking has been replaced by static checking done by
TypeScript.

Detecting a Preact/React functional component that does not use `propTypes` is
impossible to do with 100% accuracy. `function Foo() { return 'Hello' }`
is a perfectly valid component with no obvious Preact/React features.

Fortunately because of the way this helper is used, we can make do with an imperfect
check. If `mockImportedComponents` mocks something which is not really a
component, that mock will be overridden with a real mock later.

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.854.0 to 2.858.0.
- [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/v2.854.0...v2.858.0)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.6 to 8.2.7.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.2.6...8.2.7)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [exorcist](https://github.com/thlorenz/exorcist) from 1.0.1 to 2.0.0.
- [Release notes](https://github.com/thlorenz/exorcist/releases)
- [Commits](https://github.com/thlorenz/exorcist/compare/v1.0.1...v2.0.0)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 10.2.4 to 10.2.5.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/compare/10.2.4...10.2.5)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.3.1 to 18.3.4.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.3.1...v18.3.4)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [typescript](https://github.com/Microsoft/TypeScript) from 4.2.2 to 4.2.3.
- [Release notes](https://github.com/Microsoft/TypeScript/releases)
- [Commits](https://github.com/Microsoft/TypeScript/compare/v4.2.2...v4.2.3)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [eslint-plugin-mocha](https://github.com/lo1tuma/eslint-plugin-mocha) from 8.0.0 to 8.1.0.
- [Release notes](https://github.com/lo1tuma/eslint-plugin-mocha/releases)
- [Changelog](https://github.com/lo1tuma/eslint-plugin-mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/lo1tuma/eslint-plugin-mocha/compare/8.0.0...8.1.0)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [axe-core](https://github.com/dequelabs/axe-core) from 4.1.2 to 4.1.3.
- [Release notes](https://github.com/dequelabs/axe-core/releases)
- [Changelog](https://github.com/dequelabs/axe-core/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/dequelabs/axe-core/compare/v4.1.2...v4.1.3)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [mocha](https://github.com/mochajs/mocha) from 8.3.0 to 8.3.1.
- [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/v8.3.0...v8.3.1)
Signed-off-by: dependabot[bot] <support@github.com>

The @hypothesis/frontend-shared lives now in another repo. The
recommended way to test the package in the context of the client is
using yalc. Therefore, it is better to ignores yalc related files so
they are not committed by mistake.

Bumps [chai](https://github.com/chaijs/chai) from 4.3.1 to 4.3.3.
- [Release notes](https://github.com/chaijs/chai/releases)
- [Changelog](https://github.com/chaijs/chai/blob/main/History.md)
- [Commits](https://github.com/chaijs/chai/compare/4.3.1...4.3.3)
Signed-off-by: dependabot[bot] <support@github.com>

Check that non-empty tags are assigned when expected.

`createAnnotation` used to accept a partially filled-out annotation
object with arbitrary properties. However the argument was only ever
used to set the `$highlight` flag. Therefore we can simplify the
interface by making the method accept just a `highlight` flag instead.

 - Simplify `createAnnotation` argument

 - Add tests for handling of `highlight` option to `createAnnotation`

 - Remove the `createHighlight` method in guest as it was just a trivial
   wrapper around `createAnnotation({ highlight: true })`

Add missing tests for this critical property of new annotations. In the
process revise some variable names in `createAnnotation` that were
misleading.

Add tests for the main code paths in `Guest` that call `createAnnotation`.

Convert the `createAnnotation` method of `Guest` to use async/await
instead of manual chaining of Promise operations. This makes it easier
to follow the logic and see that document metadata is assigned to the
annotation before it is broadcast to other parts of the annotator in the
`beforeAnnotationCreated` event. It also makes it easier to external
code (eg. the tests) to determine when `createAnnotation` is "done" and
has finished updating the annotation.

 - Convert `Guest#createAnnotation` to use async/await

 - Update tests for `createAnnotation` to await the returned Promise
   instead of a fixed timeout

 - Add a missing check in `createAnnotation` tests for the argument
   passed to the `beforeAnnotationCreated` event

Open links to documents in a new tab. This is important in the Notebook
view at present to "escape" the Notebook's frame, but makes sense in
all contexts as it more closely adheres to our pattern of opening links
to external properties in new windows.

Make sure document titles that are not linked don't look like links.

Make `AnnotationTimestamps` align with changes to `ShowDocumentInfo`;
it is now a dumb component. Centralize logic in `AnnotationHeader`.

- Refactor `ShowDocumentInfo`: don't link to documents for third-party
  annotations. This is a possibly-temporary measure to prevent linking
  to documents that are not directly accessible, e.g. in an LMS context.
- Remove unnecessary forwarding of `showDocumentInfo` through several
  components.
- Centralize some logic in `AnnotationHeader` and make `ShowDocumentInfo`
  a dumb component.