[bc25] Handle transitions involving overlays.

This also removes most of the remaining references to
SceneFamilies.NotifShade and SceneFamilies.QuickSettings, which will be
deleted soon.

Bug: 359173565
Bug: 356596436
Flag: com.android.systemui.scene_container
Flag: com.android.systemui.dual_shade
Test: Manually. On a locked device, I double pressed the power button to
 show the camera app on top of the lockscreen. Pulled down one shade and
 then the other, verified that the scene container becomes visible and
 the shade overlays are shown on top of the camera app. Collapsed both,
 verified that the scene container became invisible again.
Test: Added new unit tests.
Test: Existing unit tests still pass.
Change-Id: I5e00be81c7ab29aab0e4a7fd2ddf7438c1178278