20488 Fix unoptimized fuchsia builds (cla: yes)

20492 Enable iOS plumbing for network security and add tests (cla: yes, platform-ios)

20494 Remove doc comments in copied web interfaces (cla: yes)

20500 Create PlatformView instance right after method channel call from Dart (cla: yes, platform-android, waiting for tree to go green)

20501 Fix the legacy EncodableValue codepaths (cla: yes)

20505 Add missing nullable annotation (cla: yes, platform-android, waiting for tree to go green)

20511 Flutter 1.21 candidate.10 (cla: yes)

20516 Missing default focus when navigating to a page with no SemanticsNode that sets namesRoute:true (cla: yes, platform-android, waiting for tree to go green)