Set Avatar Icon in Status Bar

We are setting the asssitant icon in the status bar. Now the
VisualQueryDetectionService icon would show only in pixel tablets, in
the status bar and dream overlay.

Lock Screen: https://screenshot.googleplex.com/ApkP4evCjtnEfdQ
Dream Overlay: https://screenshot.googleplex.com/4nuxBmj8a968vBH

Bug: 297985301
Test: Manual
Flag: N/A
Change-Id: If3a5041e62632e7718a58658a8a12fb021d12b60