[CS] 3/ Move isStatusBarFullscreen tracking to repo.

Bug: 300519002
Test: start ongoing call then enter immersive mode in an app -> verify
status bar still displays
Test: start ongoing call, then enter immersive mode, then swipe up to
dismiss status bar -> verify status bar disappears
Test: smoke test of the ongoing call chip
Test: atest StatusBarModeRepositoryImplTest OngoingCallControllerTest

Change-Id: I300040611746866ca474a16008918fe7cd1d38d9