Keep notif bounds stable on LOCKSCREEN->AOD

This was still a bit unpolished if media was playing
and no other smartspace content existed.

Fixes: 354392838
Test: manual - use media and go to AOD
Test: atest SharedNotificationContainerViewModelTest
Flag: com.android.systemui.migrate_clocks_to_blueprint
Change-Id: Iad2302add25498a297c4ef95c97a899bddda1922