[Dual Shade] Apply notification clipping to shade bounds in Dual Shade.

Fix: 388475946
Fix: 391379412
Test: Manually by opening and scrolling the notifications shade on both
 narrow and wide screens, and ensuring they are clipped below the clock.
Test: Added a unit test scenario.
Test: Existing unit tests still pass.
Flag: com.android.systemui.scene_container
Change-Id: Id68f9a078c6e9328961ce907941cbf41d0169750