[BREAKING CHANGE] Emit a single event from confirmation dialog

Instead of 'ok' and 'cancel', just emit 'done'. This allows us to use
.once, per Roan on Iabf0c0d0.

Bug: 65571
Change-Id: I4f485d4fa4b143868cd587ebf1edf20acaf4568f
Merge "[BREAKING CHANGE] Emit a single event from confirmation dialog"