21978 Roll Dart SDK from 5c59a47beda7 to 902538ea56d5 (2 revisions) (cla: yes, waiting for tree to go green)

21979 Reland: Use dispatchKeyEventPreIme, and handle keys sent to InputConnection.sendKeyEvent on Android (cla: yes, platform-android)

21980 Fix native constructor of list of zircon handles and remove unused list factory specializations. (cla: yes, waiting for tree to go green)

21981 Roll Dart SDK from 902538ea56d5 to fc82eeed7df3 (1 revision) (cla: yes, waiting for tree to go green)

21982 Roll Fuchsia Mac SDK from MR_bRfe8I… to pZ9FgVZTK… (cla: yes, waiting for tree to go green)