Update DreamService -> DreamOverlayService connection to handle crashes

This change implements PersistentServiceConnection and
ObservableServiceConnection helper classes in framework for better
handling of crashes.

Fixes: 247103878
Test: manually by crashing systemui using adb while dreaming and
verifying that the overlay is visible
Test: atest com.android.internal.util.PersistentServiceConnectionTest
Test: atest com.android.internal.util.ObservableServiceConnectionTest

Change-Id: Ib9a7e8675e408c1724567335a3c186fe5c9f5f59