4/ Keep EdgeBackGestureHandler state across nav/taskbar changes

- Don't update the edge back handler state when switching between nav
  and taskbar (since the nav mode doesn't change and a bar still exists
  across the change)

Bug: 219035565
Test: atest NavBarHelperTests
Test: atest SystemUITests
Change-Id: If930d8950e5cc19eb8d6e86f01b676c1acabbe2b