20681 fuchsia: Fix elevation issues (affects: engine, cla: yes, platform-fuchsia)

20697 fuchsia: Disable flaky test (affects: tests, cla: yes, platform-fuchsia)

20699 fuchsia: Rollback broken SDK and re-enable test (affects: tests, cla: yes, platform-fuchsia)

20700 Avoid passing nil to IOS accessibility announcement  (cla: yes, platform-ios, waiting for tree to go green)

20701 Ignore calls to AccessibilityBridge listeners after release (cla: yes, platform-android)

20704 fuchsia: Clean shell_unittests under FEMU (affects: tests, cla: yes, platform-fuchsia)