StatusBar icons are GONE when status bar is hidden

Explicitly disable status bar icons when the status bar isn't in view.
This is to ensure the status bar won't unnecessarily make calls to draw.

Also consolidates status bar disabling logic to
CollpasedStatusBarFragment (removed from BatteryMeterView +
StatusBarIconController).

Test: manual test that battery icon updates don't redraw when the status
bar isn't visible to the user in fullscreen/immersive modes
  1. Enable Developer Option "Show surface updates"
  2. Open fullscreen app
  3. adb shell cmd battery unplug/reset
  Observe: status bar doesn't redraw
Test: manually open a hierarchy viewer when the status bar is hidden in
a fullscreen/immersive app. observe the icons are GONE
Fixes: 120483410

Change-Id: I182559199b0a1f01122f0163836b7e2824f2acba