Improve transition between AOD and lockscreen when media is playing for

split shade

* hide the targets before AOD -> Lockscreen transition to avoid jump of
the media object

Bug: 174229939
Test: manual test for switching between AOD and lockscreen while media
is playing and with ring doorbell card
Test: atest CardPagerAdapterTest, BcSmartspaceViewTest

Change-Id: I9ad176b726beb2b7d7e07eb9b4c42d0f317ed53c