Update keyboard dismissal logic in the AllAppsTransitionController.

Dismissing the keyboard immediately interferes with the synchronized
keyboard animation. Instead, we wait until the end of the animation and
if it is successful (transition actually happened and wasn't
interrupted) we hide the keyboard. This call does nothing if the
keyboard was already hidden through the synchronized animation, and
hides it otherwise.

Bug: 234812580
Test: manual
Change-Id: Idabbc707dd0244bdf75316777e945624a8e8bdfc