[url_launcher_web] Update min Flutter version (flutter#4735)

[video_player] Wait to initialize m3u8 videos on iOS until size is set (

flutter#4727)

[url_launcher] Mark Link as an invisible factory (flutter#4578)

[shared_preferences] Documentation update for Readme.md (flutter#4684)

[image_picker] Fix NSNull handling on iOS (flutter#4728)

[camera]writing file on background queue (flutter#4721)

[camera_windows] Support camera on windows desktop platform (flutter#…

…4641)

This PR adds a Windows Desktop implementation of [camera plugin](https://pub.dev/packages/camera) using Media Foundation and CaptureEngine interface.

The implementation supports multiple cameras, video preview, and capturing photos and videos. Works with camera plugin and [camera example](https://pub.dev/packages/camera/example).

The current implementation uses FlutterDesktopPixelBuffer, but could be switched to use shared textures or Platform views after those are supported.

Unit tests are partially done; for the CaptureControllerImpl class all falilure code paths are not yet covered.

Still missing some features, like exposure and focus controls. These can be done later with interfaces IAMCameraControl and IAMVideoProcAmp,

Resolves flutter/flutter#41709: [camera] Add Windows support

[video_player] Publish fully federation version (flutter#4724)

[video_player] Federate mobile implementations (flutter#4712)

Moves the iOS and Android implementations to their own federated packages. The iOS implementation package uses the name `avfoundation` rather than `ios` since it is likely that a macOS implementation could share a significant amount of code.

As part of the federation, migrates the mobile implementations to using in-package method channels rather than the shared method channel. Currently these are just duplicates of the existing method channels; updating them to new version of Pigeon will be done in a separate PR later.

Temporarily marks `video_player` as unpublishable to allow the implementations to be moved, rather than copied and deleted, in order to better preserve git history. A follow-up PR will restore it to publishable form.

No version change: The changes to `video_player_platform_interface` only affect development of the plugin, not use of the plugin.

Part of flutter/flutter#68498
Part of flutter/flutter#94224

[video_player] Federate mobile implementations (flutter#4712)

Moves the iOS and Android implementations to their own federated packages. The iOS implementation package uses the name `avfoundation` rather than `ios` since it is likely that a macOS implementation could share a significant amount of code.

As part of the federation, migrates the mobile implementations to using in-package method channels rather than the shared method channel. Currently these are just duplicates of the existing method channels; updating them to new version of Pigeon will be done in a separate PR later.

Temporarily marks `video_player` as unpublishable to allow the implementations to be moved, rather than copied and deleted, in order to better preserve git history. A follow-up PR will restore it to publishable form.

No version change: The changes to `video_player_platform_interface` only affect development of the plugin, not use of the plugin.

Part of flutter/flutter#68498
Part of flutter/flutter#94224