Bring back Keyguard CANNED_UNLOCK_START_DELAY wait

This was taken out in I7bc350689affde76f9d3427ea94ff31f56bb75f0 because
I didn't think it was necessary, but it skipped over the "widgets going
away" animation inside the notification shade, so we really need it.

Bug: 281859780
Bug: 283077960
Test: atest KeyguardUnlockAnimationControllerTest
Change-Id: Id4db8771c668767d0c0738c486dd7c711a4941ea