[image_picker] Fixes activity leak (flutter#4439)

[ci] Run analysis with older versions of Flutter (flutter#5000)

[video_player] Add new option for allowBackgroundPlayback (flutter#5013)

[camera] Fix for CameraAccessException that prevents image capture on…

… certain devices running Android 7/8 (flutter#4572)

[camera]remove CAS operation and use dispatch queue instead (flutter#…

…4973)

[quick_actions] Publish federated version (flutter#5005)

[file_selector] Endorse macOS (flutter#5001)

[file_selector] Add macOS support (flutter#4381)

Brings file_selector_macos into flutter/plugins from FDE, with the following changes:
- Refactored slightly to allow for unit tests of almost all of the native code
- Added native unit test coverage
- Translated to Swift, to follow repo conventions for macOS plugins
- Added an in-package example (almost an exact duplicate of the app-facing version, but written against the platform interface, as is our current practice)
- Moved to an in-package method channel. As part of that, moved the flattening of type groups from Swift to Dart.

Does not currently include native UI tests to allow for end-to-end testing (since Flutter integration tests can't be used). They should be added later (they are currently blocked on flutter/flutter#90673), but the unit tests give substantial coverage, making it substantially better to move the plugin now to get those tests running.

macOS portion of flutter/flutter#70221

[in_app_purchase] Update app-facing package to new analysis options (f…

…lutter#4969)

[google_maps_flutter] Switch app-facing package to new analysis optio…

…ns (flutter#4716)