[Status Bar Refactor] Move logic about hiding status bar icons for

bouncer into a separate class and reference that in
CollapsedStatusBarFragment.

This may be a bit of a heavy-handed way of removing the StatusBar
reference from CollapsedStatusBarFragment, but I think the dedicated
class makes the logic super obvious and easy to dump for bug reports.

Bug: 204792508
Test: manual
Test: atest SystemUITests
Test: Will add new unit tests if general structure is approved
Change-Id: Ia8c4ddd84c20ca4a4e31b8079e56cbf3867efc79