Make system bars appearence logic more generic (3/N)

Update DisplayPolicy to cache app-windows that are overlapping with
status bar instead of checking specific windowing modes to determine
appearance regions of status bar.

Bug: 179251684
Test: atest DisplayPolicyTests
Test: check the status bar has proper appearance while split activated.

Change-Id: Id69a8dadcf9044fb2cde1b50108479a4375332be