Let top-fullscreen-app window keep controlling status bar

If a top-fullscreen-app window is hiding status bar but the focus is
changed to a non-fullscreen window, we let the top-fullscreen-app window
keep controlling status bar. This CL makes the logic compatible with the
legacy insets mode.

Fix: 156322689
Test: WindowInsetsControllerTests
Change-Id: I74387c2c794c8a5a7056eea3ba4ec7257c66652a