Support transitioning from doze to dream from button press.

This changelist enables going directly from dozing to dreaming from a
power button press. This is accomplished by initiating a dream rather
than waking up. Transitions are suppressed in SystemUI by tracking
the wake reason.

Test: atest DozingToDreamingTransitionViewModelTest
Bug: 389155961
Flag: com.android.systemui.glanceable_hub_v2
Change-Id: Id7621b5466caec2863e76e0257197afa86a4064c