26756 Delete window_hooks_integration_test.dart (cla: yes, waiting for tree to go green, tech-debt)

26825 Migrate //testing to nullsafety (cla: yes, waiting for tree to go green, tech-debt)

26828 Remove outdated annotations from fixtures (cla: yes, waiting for tree to go green, tech-debt, embedder)

26892 fix javadoc (platform-android, affects: docs, cla: yes, waiting for tree to go green, tech-debt)

27241 Migrate non-scenic-based fuchsia tests to cfv2. (affects: tests, cla: yes, platform-fuchsia, tech-debt)