[flexiglass] Send scroll from NSSL to flexiglass when bottom notif expands

When a notification expansion hits the bottom of the screen, we need to scroll the notif stack and scrim up to make room for the notification to fully expand. This means there needs to be a way for NSSL to pass scrolling delta to flexiglass to cover this specific case (NSSL does not reposition itself based off this delta - it waits for flexiglass to tell it how to move after having consumed the delta).

Bug: 296118689
Test: manual
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Change-Id: Ie7b43dbcd372c422259915457261e946a387234a