74355 [flutter_releases] Flutter Stable 1.22.6 Framework Cherrypicks (cla: yes, engine, tool)

74401 Cherrypick engine to 78200e894425e978bacba54320ef63e570af234a (cla: yes, engine)

74572 Cherrypick engine to 5c9b34399c2a4c6087feeae81f710fe7651568f5 (cla: yes, engine)

a: accessibility - 46 pull request(s)

62616 Migrate foundation test to nullsafety (a: accessibility, a: null-safety, cla: yes, framework)