WindowInsetsLayoutTests: Launch TestActivity in fullscreen mode

To test the system bar insets, WindowInsetsLayoutTests assert that the
activity size matches the size of the display. This is true in
fullscreen windowing mode, but is not necessarily true in other
windowing modes like freeform, where the window size can differ from the
display size.

We launch the TestActivity in fullscreen windowing mode to fulfill the
assumption that the window size will always be the same as the display
size.

Bug: 168783728
Test: atest android.server.wm.WindowInsetsLayoutTests
Change-Id: Ie575fdaf6884497d125ab024b87ed09e085c6502
3 files changed