Implement new SYSTEM_UI_FLAG_IMMERSIVE_STICKY.

Migrate transient bar mode to IMMERSIVE_STICKY, and
introduce new behavior for IMMERSIVE: namely the
opaque bars are revealed by clearing the flags on swipe.

Remove low-profile optimization that confuses api demos
and other apps using low-profile as a signal.

TransientNavigationConfirmation renamed to
ImmersiveModeConfirmation, and its associated resources,
since the confirmation is now shown when the nav bar is
shown in either of the two immersive modes.

Remove unused Toast.makeBar and associated hidden framework
bits now that the confirmation uses a cling instead.

Bug:11062108
Change-Id: Iae49d31973940b9bee9f5b1827756db5eaa76aa3