25381 fuchsia: Reliably pass View insets (cla: yes, platform-fuchsia)

25385 [fuchsia] Use scenic allocator service (cla: yes, platform-fuchsia)

25389 [iOS] Fixes context memory leaks when using Metal (platform-ios, cla: yes, waiting for tree to go green)

25395 Deduplicate plugin registration logic and make error logs visible - take 2 (platform-android, cla: yes, waiting for tree to go green)

25412 Windows: Add support for engine switches for WinUWP target (cla: yes, waiting for tree to go green, platform-windows)

25446 [iOS] Make FlutterEngine new method available (platform-ios, cla: yes, waiting for tree to go green)