29566 Hide a11y elements when resigning active (platform-ios, cla: yes)

29623 Fix iOS embedder memory management and other analyzer warnings (platform-ios, cla: yes, waiting for tree to go green)

29638 [Embedder] Send key data through message channel (platform-ios, cla: yes, platform-web, platform-fuchsia, embedder)

29665 iOS Background Platform Channels (platform-ios, cla: yes, waiting for tree to go green, platform-macos)

29723 Fix ‘google-readability-braces-around-statements’ analyzer warning in macOS and iOS (platform-ios, cla: yes, platform-macos)

29725 Cherrypick of PR flutter/engine/pull/29531 (platform-ios, cla: yes)