Bouncer notification and QS scrim

Show front scrim when the notification panel is expanded,
otherwise pin would be overlayed on top of notifications.

Change-Id: Ia438f4a2794eb9510ec05ad86cc8c19e2e716358
Fixes: 74550013
Test: double tap on notification when locked
Test: tap on QS edit button when locked
Test: unlock by swipping up
Test: fling quickly on keyguard