Correct AppWidget layout when WP is off

When the work profile (WP) is off, the layout of the widget is provided
by the system.

The layout must have a background with android:id/background as view id
and clip its outline, or it will be considered "legacy" and have the
wrong outline when moved.

Bug: 187907544
Test: Add a widget for the WP and turn the WP off.
Change-Id: Ibee31f5f0e510313ae7f8dc78c208c45a4d0e1fd