Disable unauthenticated annotating and highlighting

Address remaining contrast nits

We’ve decided not to remedy this for now, as the `disabled` state
and other attributes of the publish button suffice, but in the future
it would be good to find a better contrast solution here.

Increase contrast in annotation cards to meet WCAG AA requirements

Increase contrast of Button components (a11y)

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.619.0 to 2.620.0.
- [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/v2.619.0...v2.620.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Assume white background by default in a11y tests

Add `lang=""` to user-generated/chosen content in sidebar UI

Do not set "aria-pressed" attribute for non-toggle buttons

Several accessibility tests were failing incorrectly because axe-core
compared the component's foreground text color against the #ececec color
used for the body of the sidebar app, whereas the components are in fact
rendered on a white background.

Change a11y tests to assume a white background by default, as that is
the case for _most_ elements in the UI. Individual a11y tests can customize
this as appropriate.

Tag suggestions are user-supplied content, so indicate that language is
unknown/may differ from the UI.

Setting the `aria-pressed` attribute on a button indicates to assistive
technology that it is a toggle button. Because the `Button` component
always set this attribute and the `isActive` prop had a default value of
false, this meant that every `Button` in the UI was identified as a
toggle button by screen readers.

Fix the issue by renaming `isActive` to `isPressed` and aligning it with
the behavior of `aria-pressed`:

 - If `true`, the button is a pressed toggle button
 - If `false`, the button is a non-pressed toggle button
 - If undefined, the button is a regular button and `aria-pressed` is
   not set

Add accessible label to annotation body markdown editor

Extract repeated references to editor text string into a variable to
make it more obvious how different statements in the test are connected.

Add accessible label to search input field

Bump postcss from 7.0.26 to 7.0.27

Bumps [babel-plugin-mockable-imports](https://github.com/robertknight/babel-plugin-mockable-imports) from 1.7.0 to 1.7.1.
- [Release notes](https://github.com/robertknight/babel-plugin-mockable-imports/releases)
- [Changelog](https://github.com/robertknight/babel-plugin-mockable-imports/blob/master/CHANGELOG.md)
- [Commits](https://github.com/robertknight/babel-plugin-mockable-imports/compare/v1.7.0...v1.7.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.26 to 7.0.27.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/7.0.26...7.0.27)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump preact from 10.3.1 to 10.3.2

Bump axe-core from 3.4.2 to 3.5.1

Bump npm-packlist from 2.0.3 to 2.1.0

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.614.0 to 2.619.0.
- [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/v2.614.0...v2.619.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump request from 2.88.0 to 2.88.2

The a11y test failures were fixed in 2c96ef64.

Bumps [request](https://github.com/request/request) from 2.88.0 to 2.88.2.
- [Release notes](https://github.com/request/request/releases)
- [Changelog](https://github.com/request/request/blob/master/CHANGELOG.md)
- [Commits](https://github.com/request/request/commits)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [axe-core](https://github.com/dequelabs/axe-core) from 3.4.2 to 3.5.1.
- [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/v3.4.2...v3.5.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [preact](https://github.com/preactjs/preact) from 10.3.1 to 10.3.2.
- [Release notes](https://github.com/preactjs/preact/releases)
- [Commits](https://github.com/preactjs/preact/compare/10.3.1...10.3.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [npm-packlist](https://github.com/npm/npm-packlist) from 2.0.3 to 2.1.0.
- [Release notes](https://github.com/npm/npm-packlist/releases)
- [Commits](https://github.com/npm/npm-packlist/compare/v2.0.3...v2.1.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Add a `lang=""` attribute to the annotation quote, body and tag list in
the UI which display content chosen or generated by the user, to
indicate to the user agent that the language is unknown and may be
different than the client UI, which is currently always English.

Part of https://github.com/hypothesis/client/issues/1794.

In my testing with screen readers the meaning was reasonably clear from
the fact that you had to click on a button labeled "Search annotations"
to focus the field and there is a "Search..." placeholder. Nevertheless,
this keeps automated checking tools happy.

A better solution would probably be to re-design the search UI so that there is
enough space for a visible label and information about the search
syntax, as well as enough space for the search field on smaller screens.

Visually I think the purpose of this field is obvious without an explicit label
but it may not be clear to assistive tech users.

Fix a11y for LoggedOutMessage

Enable debugging info for JSX elements in dev builds and tests

Add reply capability to service, `AnnotationOmega`