[google_sign_in] Bridge google_sign_in and googleapis. (flutter#2824)

Introduce the first version of the `extension_google_sign_in_as_googleapis_auth` package.

This package lets users of the `google_sign_in` plugin to create an authenticated HTTP clients (from `googleapis_auth`) that can access any APIs from the `googleapis` package.

[connectivity_for_web] Fix JS Interop in release mode. (flutter#2869)

* Switch to dart:html window.navigator.connection instead of package:js JS-interop.
* Overwrite connection.onchange instead of listening to connection.onChange Stream (prevents multiple subscriptions after hot-reload).
* Cleaned up old code related to generating the JS facade.

[shared_preferences] Shared preferences linux endorsement (flutter#2864)

Endorses shared_preferences_linux.

Since shared_preferences_linux is pure Dart, this uses manual registration of the Linux implementation. It is similar to the solution used for path_provider, but improves on it by more narrowly tailoring the registration to cases where another registration hasn't already been done, and only checking the first time, thus avoiding the need for a variable to override it.

Updates shared_preferences_linux to depend on path_provider_linux rather than path_provider, to avoid adding unnecessary native plugin dependencies to other platforms.

Also adds a driver test for shared_preference_linux, which I missed in reviewing the initial shared_preferences_linux landing.

[shared_preferences] Shared preferences linux endorsement (flutter#2864)

Endorses shared_preferences_linux.

Since shared_preferences_linux is pure Dart, this uses manual registration of the Linux implementation. It is similar to the solution used for path_provider, but improves on it by more narrowly tailoring the registration to cases where another registration hasn't already been done, and only checking the first time, thus avoiding the need for a variable to override it.

Updates shared_preferences_linux to depend on path_provider_linux rather than path_provider, to avoid adding unnecessary native plugin dependencies to other platforms.

Also adds a driver test for shared_preference_linux, which I missed in reviewing the initial shared_preferences_linux landing.

[shared_preferences_linux] Add iOS stub (flutter#2865)

Add missing iOS stub to shared_preferences_linux

[url_launcher] Endorse url_launcher_linux (flutter#2863)

Adds an endorsement for url_launcher_linux, so that Linux is supported
automatically.

Part of flutter/flutter#41721

[url_launcher] Endorse url_launcher_linux (flutter#2863)

Adds an endorsement for url_launcher_linux, so that Linux is supported
automatically.

Part of flutter/flutter#41721

[url_launcher_linux] Add Linux url_launcher plugin (flutter#2857)

Adds url_launcher_linux, the federated implementation of url_launcher.

Not yet endorsed by url_launcher

Part of flutter/flutter#41721

[image_picker] updated VALID_ARCHS to support iPhone simulator (flutt…

…er#2761)

[multiple] Improve video playback in image_picker example (flutter#2819)

This change adds small bugfixes to the following packages:

* video_player_web:
  * Prevent parsing Blob URLs so Safari can play from a PickedFile.
  * Allow users to 'mute' videos by setting their volume to 0.0 (this enables auto-play in most modern browsers)
* video_player:
  * Fix an issue where aspect ratio calculations failed when some of the video sizes were zero (happened in web for incorrect videos)
* image_picker (example app):
  * Start videos in web muted so they can auto-play
  * Dispose video controllers when they're really not needed. This fixes a fatal crash in Safari (not so fatal in other browsers).