Let action bar background extend into system insets

This CL makes action bar background extend into system insets if the
content view doesn't fit any insets.

Bug: 343131420
Bug: 309578419
Flag: com.android.window.flags.enforce_edge_to_edge
Test: atest ActionBarOverlayLayoutTest
Change-Id: I266e55fce8e5a387ae0b56f7c22756d9ec153611