25453 Add automatic onBackPressed behavior to FlutterFragment (platform-android, cla: yes)

25465 Forward a11y methods from FlutterSwitchSemanticsObject (platform-ios, cla: yes, waiting for tree to go green)

25474 Roll Fuchsia Linux SDK from 0Db2pEb0U… to R3xv3K9Hz… (cla: yes, waiting for tree to go green)

25476 Roll Fuchsia Mac SDK from a9NOB6sdo… to eV1E54W8a… (cla: yes, waiting for tree to go green)

25477 Windows: Only terminate display for last instance (cla: yes, waiting for tree to go green, platform-windows)