Re-land: Enable prefer_mixin and bump plugin_platform_interface to 2.1.7 (#5841)

This reverts commit flutter/packages@5aef49b, except for the Flutter version pin, thus re-landing flutter/packages#5793. Now that the tree is fixed, it can be re-landed for auto-publishing.

Author: stuartmorgan-g

CHANGELOG.md

@@ -1,5 +1,6 @@
-## NEXT
+## 6.2.2
 
+* Updates minimum required plugin_platform_interface version to 2.1.7.
 * Updates minimum supported SDK version to Flutter 3.10/Dart 3.0.
 
 ## 6.2.1

pubspec.yaml

@@ -4,7 +4,7 @@ repository: https://github.com/flutter/packages/tree/main/packages/video_player/
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+video_player%22
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 6.2.1
+version: 6.2.2
 
 environment:
   sdk: ">=3.0.0 <4.0.0"
@@ -13,7 +13,7 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  plugin_platform_interface: ^2.1.0
+  plugin_platform_interface: ^2.1.7
 
 dev_dependencies:
   flutter_test: