Use KeyguardTransitions instead of PowerInteractor's wakefulness state

PowerInteractor#finishedGoingToSleep doesn't actually mean the
screen finished turning off. Instead, let's rely on KeyguardTransitions
which, when the current state is updated to AOD/off/dozing, the
screen has finished turning off.

Bug: 225183106
Flag: ACONFIG com.android.systemui.udfps_view_performance DEVELOPMENT
Test: atest UdfpsControllerOverlayTest
Change-Id: I74d30d83fb9e6e9cdb4fe26aa755638b924f0371