TRDS: Fix Volume panel background

Volume panel is a bit out of the box compared to the normal theming.
Reapply the background via java code on theme change.

Change-Id: I0df41a95487f7c23d5fda5c2ec7df763c8e2f466

Conflicts:
	core/java/android/view/VolumePanel.java
	core/res/res/values/slim_symbols.xml