[CS] Have SBNotifActivityStarter use KeyguardStateController#isOccluded.

CentralSurfacesImpl#isOccluded just delegates to KeyguardStateController
under-the-hood, so the activity starter can use KSC directly.

Bug: 277764509
Test: manual: verified via logging that SBNAS receives correct
isOccluded value when a notification is clicked (true if HUN appears on
top of occluding activity like camera, false otherwise)

Test: atest StatusBarNotificationActivityStarterTest
Change-Id: If9d37bd308306a36ea296688406436b6511da26a