23499 Adds a mechanism for announce events to be forwarded to a11y. (cla: yes, waiting for tree to go green)

23503 During image decoding, avoid using smart pointers for DartWrappables that cross thread-boundaries. (cla: yes, waiting for tree to go green)

23504 Make pending event handling more lenient to allow out of order responses (cla: yes)

23506 Revert “bump fuchsia toolchain to clang-12” (#23456) (cla: yes)

23508 Started sharing skia contexts on the io thread (cla: yes)

23509 Roll Fuchsia Mac SDK from cLR0CUb-e… to IGtSAREVb… (cla: yes, waiting for tree to go green)