Let WindowInsetsTests support edge-to-edge

This CL lets the activities handle insets properly because apps
targeting V are forced to go edge-to-edge.

This CL also lets the app support dark theme.

Fix: 329647020
Bug: 309578419
Test: Open each activity with or without dark theme, and see if the
      layout and the color are correct.
Change-Id: I159a042e546a60c33bd0e2fb3b66736501386979