Depends on D19245. Fixes T11145. Ref T13108. See PHI488. Disable workflow buttons when they're clicked to prevent accidental client-side double submission.

This might have some weird side effects but we should normally never need to re-use a workflow dialog form so it's not immediately obvious that this can break anything.

• Added sleep(1) to the Mute controller and the Maniphest task controller.
• Added phlog(...) to the Mute controller.
• Opened the mute dialog, mashed the button a thousand times.
  • Before: Saw a bunch of logs.
  • After: Button immediately disables, saw only one log.