Switch TitleKey to use TitleMoveCompleting hook

This keeps the titlekey update inside the main transaction so it
doesn't get lost in post-edit updates. Should improve consistency
in case of unexpected failures, and may also help in places where
the deferred updates are run in odd ways.

Bug: T148860
Change-Id: Iff51e928456d04889232f8a18dd1fdfb2a9d541e