25843 [flutter_releases] Flutter Stable 2.0.6 Engine Cherrypicks (platform-ios, platform-android, cla: yes, platform-web, platform-macos, platform-linux, platform-windows, platform-fuchsia, embedder)

25860 Moved PlatformMessage’s to unique_ptrs (platform-ios, platform-android, cla: yes, waiting for tree to go green, platform-fuchsia, embedder)

25867 Switch PlatformMessages to hold data in Mappings (platform-ios, platform-android, cla: yes, platform-macos, platform-fuchsia, embedder)

25961 Hardware Keyboard: iOS (platform-ios, cla: yes, platform-macos, embedder)