[Notif] Add real Kosmos implementations for HeadsUpManager + related

The real Kosmos.headsUpManager isn't used anywhere right now because all
the classes using Kosmos.mockHeadsUpManager were using mock-related
methods. But at least it will exist for future tests?

Bug: 378142453
Test: atest HeadsUpAppearanceControllerTest
Flag: TEST_ONLY
Change-Id: If7fe46a5bb7b348c536ced1ce3a2e40752dae8aa