Have responsive taskbar UI during swipe up gesture.

- Makes taskbar threshold an absolute Y threshold
  instead of a distance threshold.
- Moves handle, taskbar view, and taskbar background
  during the swipe up gesture

Next CL will address transforming the nav handle <-> taskbar
and ensuring that there's a clean handoff

Bug: 246631059
Test: swipe up on taskbar, release. see bounce
      swipe up on taskbar to go home, proper icon alignment
      swipe up on taskbar, pause for overview, see bounce
      -> further movement should not move taskbar
      test launcher3

Change-Id: I141236fd72428cda7edd0ff116de1d478d18c722