19499 Flutter 1.20 candidate.3 (cla: yes)

19500 fuchsia: Remove dead flutter_frontend_server code (cla: yes, code health, platform-fuchsia)

19502 Roll Skia from 733666b3be3b to 52a4379f03f7 (1 revision) (cla: yes, waiting for tree to go green)

19505 Roll Fuchsia Mac SDK from s4lA_… to _Na1L… (cla: yes, waiting for tree to go green)

19506 Roll Fuchsia Linux SDK from tu9Py… to TizBd… (cla: yes, waiting for tree to go green)