[Status Bar] Delay showing the status bar until occlusion finishes.

Bug: 273314977
Change-Id: I3d08d32c2a390abe84317924156e8dbffd271004
--- manual tests ---
Test: launch fullscreen activity over lockscreen -> status bar never
shows up
Test: launch non-fullscreen activity over lockscreen -> status bar fades
in once activity launches
Test: launch camera over lockscreen -> status bar never shows up
Test: launch camera over bouncer -> status bar never shows up
Test: launch non-fullscreen activity over bouncer -> status bar appears
Test: launch fullscreen activity over bouncer -> status bar never shows
up
Test: on lockscreen, click power button to trigger dream -> left-hand
side of status bar never flickers
Test: no status bar on bouncer
Test: after unlock, open fullscreen app -> verify status bar doesn't
appear. Then, swipe down from top -> verify status bar appears
Test: HUN on lockscreen -> no status bar changes
Test: HUN on homescreen -> status bar shows HUN app name only

Test: general verification that status bar appears at the right times

--- unit tests ---
Test: atest CollapsedStatusBarFragmentTest
Test: atest CollapsedStatusBarViewModelImplTest

Change-Id: I0ddf379dd84afd2b51ec8705648f45c1158cfc84