[flexiglass] Hide surface under keyguard during swipe

We now wait until the user lifts their finger before revealing the
surface underneath lockscreen.

Flag: com.android.systemui.scene_container DEVELOPMENT
Bug: 344844978
Test: manual
 0. Enable flexiglass
 1. Swipe up on the keyguard, do not lift finger.
 Observe: launcher does not appear
 2. Release finger
 Observe: launcher appears
Change-Id: Ic7ea906efaab486c08f03e3aea2172469351f8d2