[DO NOT MERGE] OCCLUDED->LOCKSCREEN transition

Follow the same path as DREAMING->LOCKSCREEN, do a subtle fade and y
translation upon unoccluding.

Allow coroutinecontext override for collectFlow, to optimize path for
transition steps.

Gated behind existing flag (223).

Test: atest OccludedToLockscreenTransitionViewModelTest
NotificationPanelViewControllerTest
Bug: 195430376

Change-Id: I3e031d7b2f72c43f5d9a93954e983c7ff6c34270