The need for this "testing only" code can be removed by improving the way
that we simulate the `connect` message being handled in tests.

Initially, I tried to if/else portions of the code to accommodate for
`MessagePort`, aiming to avoid duplication of the code (like I did for
`shared/frame-rpc.js` #3565). However, I found that, unlike
`shared/frame-rpc.js`, this resulted into a spaghetti-type of code, not
very understandable.

Then, I decided to create two internal methods to support both the
current communication using `Window` and the new `MessagePort`. This in
my opinion leads to a clearer results, although some code is duplicated
in both methods.

This PR will result on a reduction in code coverage, which will be fix
by #3590.

Bumps [karma-browserify](https://github.com/nikku/karma-browserify) from 8.0.0 to 8.1.0.
- [Release notes](https://github.com/nikku/karma-browserify/releases)
- [Commits](https://github.com/nikku/karma-browserify/compare/v8.0.0...v8.1.0)

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Bumps [@hypothesis/frontend-shared](https://github.com/hypothesis/frontend-shared) from 3.4.0 to 3.5.0.
- [Release notes](https://github.com/hypothesis/frontend-shared/releases)
- [Changelog](https://github.com/hypothesis/frontend-shared/blob/v3.5.0/CHANGELOG.md)
- [Commits](https://github.com/hypothesis/frontend-shared/compare/v3.4.0...v3.5.0)

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In addition, I simplified the execution of the callback.

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.943.0 to 2.948.0.
- [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/v2.943.0...v2.948.0)

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Bumps [axe-core](https://github.com/dequelabs/axe-core) from 4.2.3 to 4.3.1.
- [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/v4.2.3...v4.3.1)

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Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 10.3.0 to 10.3.1.
- [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/10.3.0...10.3.1)

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Bumps [eslint](https://github.com/eslint/eslint) from 7.30.0 to 7.31.0.
- [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/v7.30.0...v7.31.0)

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The word `listener` matches better the internal property names of
`this.channelListeners` and `this.onConnectListeners`. In addition, it
helps to differentiate from the `callback` function which is the last
(optional) argument of the `listener`. The `callback` is used to send
back a `postMessage` response to the other frame/s.

The RPC class design requires all the handlers to be provided up-front.
Currently, adding a new handler after a channel is created has no
effect. To make more obvious this misuse, the method now throws an
error.

`this.link` was defined as `Array<{channel: RPC, window: Window}>`
however, the `window` property was never used. I am guessing that the
original idea was to avoid creating additional channels for the same
frame, however, that was never implemented.

I take the decision of removing the `window` property and converting the
`this.link` to a type of `RPC[]`.

As far as I know, the `return` statement don't have any effect.

As pointed by @robertknight `Array.from` was probably a leftover from
the tool that was used to convert CoffeeScript to JavaScript.

I also include a minor change to improve the readability extracting the
callback from the `args`.

This reverts commit e466e836.

This reverts commit ede3280f.

The tag filter's regex was not capturing words at the start of a line which had non-word ASCII or unicode characters. Additionally it was not escaping special chars for the regex query.

This fix first splits the tag based on words, escapes the query, searches for any match, and then additionally checks the entire tag against the query

The tag filter's regex was not capturing words at the start of a line which had non-word ASCII or unicode characters. Additionally it was not escaping special chars for the regex query.

This fix first splits the tag based on words, escapes the query, searches for any match, and then additionally checks the entire tag against the query

The regex-ex was not capturing words at the start of a line which had ASCII characters.

This fix first splits the string based on words and searches for any match and then additionally checks the entire string against the query

This method is available after including the `dom.iterable` typings.
Also the use of `entries()` is unnecessary because the result is the
same as directly iterating over the `URLSearchParams` instance.

Also add an example for `stringify`.

For the client's very simple query string generating and parsing needs
we can avoid this dependency by using a very simple wrapper around
`URLSearchParams`. This also improves type checking since this
dependency didn't provide types and we weren't using the
@types/query-string package.

The `stringify` function sorts parameters in the returned string for
consistency with query-string's behavior.

This method was not used anywhere. In addition for this method to have
the intended effect, it needed to be called before `createChannel`,
because at that point the methods are registered with the `RPC` class
and there is no way to remove the listeners.

The `Bridge` code was written before we had good mocking tools in the
client. As a result the `Bridge` class mocks `RPC` in an unconventional
way where it constructs the real class, but then stubs out specific
methods. Also tests varied in the degree to which they tested only
`Bridge` vs Bridge + RPC together.

This commit mocks `RPC` in bridge-test.js using our standard mocking
tools and makes all tests in the file unit tests. This involved some
significant changes to the `onConnect` tests.

* change `@deprecated` for a comment
* added a test to cover some missing lines in `_isValidSender` function.
* `_isValidMessage` renamed to `_parseMessage`
* created helper function `waitForMessageDelivery`
* parametrise test

RPC:
* added `@deprecated` statements and additional comments
* removed `this._destroyed` for the listener checks, because the
  listener is removed when called `destroy()`.
* added `this._port.close()` in addition to removing the listner.

`bridge-test`:
* refactor all the `function () {}` to arrow functions

`frame-rpc-test.js`:
* added these tests to check the `MessageChannel` functionality.

Created a couple of utility methods to avoid duplication of code and
enable to decouple RPC for `Window` or for `MessagePort`.

It simplifies the code.

It is a bit of a Frankenstein. The plan is to clean up on the next
commits.

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.939.0 to 2.943.0.
- [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/v2.939.0...v2.943.0)

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Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.2.9 to 2.3.0.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/2.2.9...2.3.0)

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Bumps [sass](https://github.com/sass/dart-sass) from 1.35.1 to 1.35.2.
- [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/1.35.1...1.35.2)

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Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 6.8.0 to 6.9.0.
- [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/6.8.0...6.9.0)

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Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 10.2.6 to 10.3.0.
- [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/10.2.6...10.3.0)

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Per WCAG 2.1 criterion: 2.5.3 Label in Name--we should not differentiate between the aria-label and the visual name in an input element. In the case of the TagEditor, the `placeholder` and `aria-label` were different. The simple fix is to remove `aria-label`.

The second problem is with AnnotationPublishControl's button where the `aria-label` and button's text did not match. Again, the simple fix is to remove `aria-label`.

Enforce the use of object shorthand syntax everywhere for consistency.
eg. `{ foo }` instead of `{ foo: foo }`. We had already converted most
occurrences manually.

We've been gradually converting anonymous functions to arrow functions
since adopting ES6. This commit uses ESLint to finish the process by
converting the remaining non-named, non-`this`-using callbacks to arrow
functions.

 - Enable `prefer-arrow-callbacks` lint rule. The `allowNamedFunctions`
   option is enabled because we have a few instances (eg. in
   gulpfile.js) of explicitly naming functions for use in debugging /
   logging etc.

 - Run `eslint --fix .` and `yarn format` to automatically fix up the
   code