Block background dream launch during widget launch and occlusion.

This changelist restricts restarting dreams behind the glanceable hub
if a widget is launching an activity. It also uses the keyguard
occlusion signal from keyguard interactor as another restriction, as
this value is often more current than the KeyguardState.

Test: atest CommunalDreamStartableTest#shouldNotStartDreamWhenLaunchingWidget
Test: atest CommunalDreamStartableTest#shouldNotStartDreamWhenOccluded
Fixes: 364522347
Flag: EXEMPT bugfix
Change-Id: I18ca19f424214191d61fdcfd170314bb351d3732