28859 Roll Fuchsia Mac SDK from AaBCvnaBN… to OPoARlWlE… (cla: yes, waiting for tree to go green)

28863 [fuchsia] Remove unused deps on fidl optional.h. (cla: yes, waiting for tree to go green, platform-fuchsia, needs tests)

28868 [iOSTextInput] remove floating cursor asserts (platform-ios, cla: yes, waiting for tree to go green)

28874 Roll Dart SDK from 9e2228a0e880 to 0cddaa9859a5 (1 revision) (cla: yes, waiting for tree to go green)

28875 Roll Fuchsia Linux SDK from Jo9QY1R3C… to UUcoJDQho… (cla: yes, waiting for tree to go green)