Add a method to go Home from immersive fullscreen app

This requires two swipes - first to bring the navbar back followed by
standard goHome() interaction.

Currently only supported in gesture nav, as with immersive landscape in
3 button navigation the swipe gesture must happen on the left/right
edge of the screen.

Bug: 300969961
Test: n/a

Change-Id: I9d6d327998d474063727acc786fe297cc2df6b62