Add OFF->LOCKSCREEN transition

Stabilize clock transitions so they do not animate, add some basic
alpha on OFF->LOCKSCREEN, and fade the content in. Do not begin
the transition until the device is ready, as opposed to during
as CoreStartable.

Fixes: 329035000
Test: atest OffToLockscreenTransitionViewModelTest
Flag: com.android.systemui.migrate_clocks_to_blueprint
Change-Id: Ibe7140fc01a9ce7decf49de875b85aca01c810cf