Rename PRIVATE_FLAG_STATUS_BAR_EXPANDED

New name: PRIVATE_FLAG_STATUS_FORCE_SHOW_NAVIGATION
This flag indicates that status bar is in a state that the user may
require navigation bar to interact with. So rename it to match its
meaning for better understanding.

Bug: 80147982
Test: 1. Launch a show-when-locked turn-screen-on immersive app on
         AOD, and see if any system bar flashes.
      2. Launch a show-when-locked turn-screen-on immersive app on
         lockscreen, and see if any system bar flashes.
      3. Launch an immersive app and drag down the status bar, see
         if nav bar keeps there as long as status bar is expanded.

Change-Id: I8870814761d798aca06d18cf0ebf7655333e7c3b