Stash taskbar if user touch down above the gesture height.

Bug: 252905206
Test: open taskbar, tap in gesture area, confirm no stash
      open taskbar, tap on taskbar item, confirm no stash
      open taskbar, tap to the side above gesture area, confirm stash

Change-Id: Ide030840440b5f0541d0ccfb055b8a8a7e851657