Add tests to cover the cases where the position is on a page before the
quote and where the position is negative.

Refactor quote anchoring logic to use async/await instead of Promise
chains to make control flow easier to follow and change.

 - Convert `getPageOffset` and `findPage` helper functions to use
   async/await rather than Promise chains.

 - Combine the `prioritizePages` and `findInPages` functions into a
   single `anchorQuote` function.

   Combining the two functions allows some redundant work to be
   eliminated. `findInPages` used to call `getPageOffset` for the
   current page on each iteration which would in turn fetch the text of
   every page until it reached the given offset. `prioritizePages` would
   do a very similar loop in order to enumerate pages close to the given
   offset.

 - Replace use of `TextQuoteAnchor.fromSelector` with direct use of
   `matchQuote`. `fromSelector` wasn't providing any value over just
   calling `matchQuote` directly, and it required a dummy DOM element to
   be created and have its text populated.

In scss files, `@use "..."` has been replaced by `@use '...'" (single
quotes instead of double).

Bumps [prettier](https://github.com/prettier/prettier) from 2.3.2 to 2.4.0.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/main/CHANGELOG.md)
- [Commits](https://github.com/prettier/prettier/compare/2.3.2...2.4.0)

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Bumps [typescript](https://github.com/Microsoft/TypeScript) from 4.4.2 to 4.4.3.
- [Release notes](https://github.com/Microsoft/TypeScript/releases)
- [Commits](https://github.com/Microsoft/TypeScript/compare/v4.4.2...v4.4.3)

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Bumps [@babel/preset-env](https://github.com/babel/babel/tree/HEAD/packages/babel-preset-env) from 7.15.4 to 7.15.6.
- [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/v7.15.6/packages/babel-preset-env)

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Bumps [sass](https://github.com/sass/dart-sass) from 1.39.0 to 1.39.2.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sass/dart-sass/compare/1.39.0...1.39.2)

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Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.983.0 to 2.987.0.
- [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/v2.983.0...v2.987.0)

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Bumps [core-js](https://github.com/zloirock/core-js) from 3.17.2 to 3.17.3.
- [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/v3.17.2...v3.17.3)

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Bumps [commander](https://github.com/tj/commander.js) from 8.1.0 to 8.2.0.
- [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/v8.1.0...v8.2.0)

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Bumps [@hypothesis/frontend-shared](https://github.com/hypothesis/frontend-shared) from 3.8.1 to 3.9.0.
- [Release notes](https://github.com/hypothesis/frontend-shared/releases)
- [Changelog](https://github.com/hypothesis/frontend-shared/blob/main/CHANGELOG.md)
- [Commits](https://github.com/hypothesis/frontend-shared/compare/v3.8.1...v3.9.0)

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In https://github.com/mozilla/pdf.js/pull/13661 the API for retrieving
PDF fingerprints (aka. File Identifiers) changed. In generic builds of
PDF.js the old API remains available, but not in the non-generic one
that Firefox's built-in viewer uses.

This commit makes Hypothesis use the new API if available or the old API
otherwise. The fingerprint value should be the same in both cases.

Fixes #3673

This is the result of running scripts/update-pdfjs.

Use async/await to simplify a test.

* rename `embedElement` to `bootScript`
* remove unused class

* Created a helper function to test the addition of the Hypothesis
  script
* Move all the helper functions before the `beforeEach`

`FrameObserver` could be disconnected while waiting for the loading of
the iframe. We add a mechanism to avoid this race condition.

Move documentation to the FrameObserver class.

As suggested here: https://github.com/hypothesis/client/pull/3670#discussion_r686665805

`_removeFrame` must be called in these three scenarios:

- `enable-annotation` attribute is removed from iframe
- `src` attribute is modified in the iframe
- iframe is deleted

When the iframe is deleted there are two possible paths for the execution of
the `_removeFrame`:

1. First and faster execution of `_removeFrame`: `iframe.remove()`
   triggers the `unload` event which calls the `_removeFrame`

2. Second and delayed execution of `_removeFrame`: `iframe.remove()`
   triggers the `MutationObserver` (debounced by 40 ms). This could
   cause the `_removeFrame` to be fired if the first path would not
   remove the iframe from the list of `_handledFrames`.

I moved the addition and deletion of the iframes to `_handledFrames` as
earlier as possible in the `_addFrame` and `_removeFrame` methods to
avoid racing conditions. A consequence of this is that the `_addFrame`
is executed only once per iframe. If it fails (for example, because the
iframe is from a different origin) it is not constantly retried.

The `FrameObserver` unit test now exercise the whole class, not just the
`findFrames` function.

On a future commit, we will inline the `findFrames functionality.

`onDocumentReady` returns now a Promise instead of calling a callback.

The name of `isDocumentReady` gives the impressiong that the function
would return a boolean.  `onDocumentReady`, on the other hand, expresses
more clearly that the execution of the callback will be triggered after
the iframe's documen is ready (loaded and parsed).

On a follow up commit I change the `onDocumentReady` to return a Promise
instead of executing a callback.

`Set` is a better data structure because it has a faster search: `Set.has` has a O(1) while `Array.includes` has a O(n).

Moved `frame-util` functionality to `frame-observer.js` and
`hypothesis-injector.js`:

- `isAccessible`, `findFrames` and `isDocumentReady` functions to
  `frame-observer.js`, and

- `hasHypothesis` and `injectHypothesis` functions to
  `hypothesis-injector.js`

Renamed and move `src/annotator/util/test/frame-util-test.js` to
`src/annotator/test/frame-observer-test.js`. This unit test only
exercise the `findFrames` function.

I run this command `prettier -w --parser html` on `shadow-dom.mustache`

In the latest version of the frontent-shared package, `extraRoute` has a
mandatory property `group` that must be either
`"home" | "foundations" | "patterns" | "components"`;

There are three ways to fix this:

* make the `group` property optional in the frontend-shared package (I
  don't know if that's a good idea).

* cast the `string` type to the one of the allowed types: `    group:
  /** @type {'components'} */ ('components'),`

* cast the `extraRoute` (this PR).

Edge 17 complains if the script is outside the body.

The current inter-frame communication doesn't work if an annotatable
(guest) iframe is from a different origin than the host frame (see
https://github.com/hypothesis/client/pull/3611#issue-696947005). This
will be fixed in a more comprehensive overhaul of the inter-face
communication (see https://github.com/hypothesis/client/issues/3533).

Meanwhile, I add a scenario into the local dev server where the
annotatable iframe is from an origin different than the host frame. For
this, I needed to spawn an additional dev server at port 3002):

```
[11:32:50] Dev web server started at http://localhost:3000/
[11:32:50] Dev web server started at http://localhost:3002/
```

Close #3629

Fix an issue where the sidebar failed to appear in Safari 11 and Chrome
63 when returning a cross-origin Window from a Promise `then` callback.
In these browsers an exception is triggered when the browser tries to
test if the return value is a Promise that can be unwrapped.

The issue was resolved in more recent browsers by adding an undefined
`then` property to cross origin objects. [1]

[1] https://github.com/whatwg/dom/issues/536

Bumps [@babel/preset-env](https://github.com/babel/babel/tree/HEAD/packages/babel-preset-env) from 7.15.0 to 7.15.4.
- [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/v7.15.4/packages/babel-preset-env)

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Bumps [@hypothesis/frontend-shared](https://github.com/hypothesis/frontend-shared) from 3.7.0 to 3.8.1.
- [Release notes](https://github.com/hypothesis/frontend-shared/releases)
- [Changelog](https://github.com/hypothesis/frontend-shared/blob/main/CHANGELOG.md)
- [Commits](https://github.com/hypothesis/frontend-shared/compare/v3.7.0...v3.8.1)

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Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 10.3.3 to 10.3.4.
- [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/10.3.3...10.3.4)

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Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.9.1 to 18.10.0.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.9.1...v18.10.0)

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Bumps [mustache-express](https://github.com/bryanburgers/node-mustache-express) from 1.3.1 to 1.3.2.
- [Release notes](https://github.com/bryanburgers/node-mustache-express/releases)
- [Commits](https://github.com/bryanburgers/node-mustache-express/commits)

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Bumps [core-js](https://github.com/zloirock/core-js) from 3.16.4 to 3.17.2.
- [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/v3.16.4...v3.17.2)

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Bumps [katex](https://github.com/KaTeX/KaTeX) from 0.13.16 to 0.13.18.
- [Release notes](https://github.com/KaTeX/KaTeX/releases)
- [Changelog](https://github.com/KaTeX/KaTeX/blob/master/CHANGELOG.md)
- [Commits](https://github.com/KaTeX/KaTeX/compare/v0.13.16...v0.13.18)

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Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.978.0 to 2.983.0.
- [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/v2.978.0...v2.983.0)

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