Workaround for back arrow being stuck on screen

- Whenever we defer the cleanup of the back gesture, schedule a failsafe
  to clean up the window if it's not handled properly.  We'll enable
  this failsafe for sc-dev and disable it for further investigations
  post sc-dev
- Dump additional info for the nav bar window so we can narrow down
  the issue post sc-dev

Bug: 190778197
Test: Can't repro the initial issue, so artificially trigger it to verify failsafe
Test: adb shell dumpsys activity service SystemUIService
Change-Id: I0a8f25babe750e6e5ba4c933ab5271a82ef63646