12375 Sync dart_runner (cla: yes)

12376 Roll Wuffs to 0.2.0-alpha.47 (cla: yes)

12380 [flutter_runner] a11y updates, tests! (CQ+1, cla: yes)

12383 Add macOS testing support (cla: yes)

12385 Reland “Smooth out iOS irregular input events delivery (#12280)” (cla: yes)

12395 Update –dart-vm-flags whitelist to include –write-service-info and –sample-buffer-duration (cla: yes)

12402 Resize channel buffers (CQ+1, cla: yes)

12403 Don’t send pointer events when the framework isn’t ready yet (cla: yes, platform-web)