9428 Update README.md for consistency with framework (cla: yes)

9431 Generate weak pointers only in the platform thread (cla: yes)

9436 Add the functionality to merge and unmerge MessageLoopTaskQueues (cla: yes)

9439 Eliminate unused import in FlutterView (cla: yes)

9446 Revert “Roll fuchsia/sdk/core/mac-amd64 from Cx51F… to e8sS_…” (cla: yes)

9449 Revert “Roll fuchsia/sdk/core/linux-amd64 from udf6w… to jQ8aw…” (cla: yes)

9450 Revert “Roll fuchsia/sdk/core/mac-amd64 from Cx51F… to w-3t4…” (cla: yes)