Convert the root `<hypothesis-app>` component to Preact and update the
startup code in `src/sidebar/index.js` to replace the AngularJS app
bootstrap with rendering the `HypothesisApp` component directly using
`render` from Preact.

This is no longer needed as we no longer have any AngularJS components
in the app.

Assorted Angular migration cleanups

Migrate `SidebarContent` to preact

Make `streamer` auto-reconnect on user change to support this migration

Avoid accessing state via `getState()`

This is needed so that `searchUris` don’t change when non-relevant
frame state changes

Add a selector to check if any annotation fetches have completed yet

Add selector to check if there are any applied filters on annotations

In preparation for the removal of angular-mocks from the codebase,
remove the final usage of it outside UI components.

Tune tutorial text to eliminate input-modality-specific instructions.

Fixes https://github.com/hypothesis/client/issues/2062

Revise re-fetching of groups when logged-in user changes

Use the dummy/blank profile object as the initial value of the `profile`
field rather than `null`. This allows us to eliminate null-checks
elsewhere while still enabling `hasFetchedProfile` to distinguish this
profile from the profile fetched from the API.

Add visibility hidden to the sidebar iframe when its closed (and after it finishes animation). This prevents all interaction from the components of the sidebar.

Add an optional coerce method to the hostPageSetting so that any incoming values can be coerced if needed. This may be required for values from from via that may only be a string type.

openSidebar config value gets coerced to a boolean in the annotator settings (just like it does in the host-config).

Redo the automatic reload of groups when the logged-in user changes:

 - Ignore the initial change of user on startup if the user is logged
   in from a previous session. This generated an unnecessary additional
   API call on startup if the user had a login from a previous session

 - Replace the use of the deprecated `USER_CHANGED` Angular event in
   favor of reacting to store state changes using
   `watch(store.subscribe, ...)`

Change the representation of the un-fetched profile within the `session`
store module to make it possible to determine whether the profile has
been fetched yet or not and expose this information via a
`hasFetchedProfile` selector. The `profile` selector continues to return
a dummy "logged out" profile before the real profile is fetched. This
simplifies some of the code that uses that selector.

This makes it possible for services to distinguish between the user ID changing
because the user logged in by clicking "Log in" and completed the login
process vs. the user already being logged in from a previous session.

Replace remaining uses angular-toastr/flash with toastMessenger

Per Lyza's suggestion and matches the examples at
https://www.typescriptlang.org/docs/handbook/type-checking-javascript-files.html

Remove unused Preact component wrappers

Fix thread list jumping when scrolling on mobile

Bump commander from 5.0.0 to 5.1.0

Bump sass from 1.26.3 to 1.26.5

Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.0.9 to 2.0.10.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/2.0.9...2.0.10)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump mocha from 7.0.1 to 7.1.2

Bumps [commander](https://github.com/tj/commander.js) from 5.0.0 to 5.1.0.
- [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/v5.0.0...v5.1.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump terser from 4.6.11 to 4.6.12

Remove old toast notifications UI and dependencies as these are no
longer used.

For certain error messages, we do not want the notice to be dismissed
automatically as either the issue prevents further usage of the client
(eg. a problem acquiring an access token when third-party accounts are
in use) or the problem is likely to happen while the user is not
interacting with the client.

Add an `autoDismiss` option to `toastMessenger` message methods and use
it when handling access token fetching errors on pages that use
third-party accounts.

Toasts in the old UI used to have a title and a message. Toasts in the
new UI currently only have a message.

Replace the last remaining uses of the old toast notification service
and UI (`flash`) with the new one (`toastMessenger`). This provides a
better-looking and accessible experience for these errors.

Work around issue with Node v14 and Puppeteer

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.660.0 to 2.663.0.
- [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/v2.660.0...v2.663.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>