[flexiglass] Unify methods to collapse the shade under ShadeInteractor.

Add functions that collapse the notifications shade and QS shade in
ShadeInteractor appropriately, whether it's Dual Shade or not.

This also adds an isNotificationsShadeExpanded flow to ShadeInteractor,
as well as overlay transition definitions for the
SlightlyFasterShadeCollapse transition key.

Bug: 356596436
Flag: com.android.systemui.scene_container
Test: Added unit tests.
Test: Existing unit tests still pass.
Change-Id: Ibaeae400c789aac148e590b0e383d0098001adea