25548 [macos] Release the copied pixel buffer after texture creation (cla: yes, waiting for tree to go green, platform-macos, embedder, cp: 2.2)

25570 Add FlutterCompositor base class (cla: yes, platform-macos)

25600 Support text editing voiceover feedback in macOS (cla: yes, waiting for tree to go green, platform-macos)

25698 fix AccessibilityBridgeMacDelegate to grab nswindow from appdelegate (cla: yes, waiting for tree to go green, platform-macos)

25790 Add a stub implementation of FlutterMetalCompositor (cla: yes, platform-macos)

25828 Correct an inverted null pointer check (cla: yes, platform-macos)