Fix animation problem when swipeing up app to screen edge and release

- Consider scroll diff between currentPage and primary scroll when calculating adjacent page offset
- Removed setEnableFreeScroll call in onPrepareGestureAnimation that calls setCurrentPage and causes jumping

Fixes: 197012570
Fixes: 195740577
Test: Swipe up from app to end of screen, adjacent task should come from screen edge, and app should snap smoothly to position
Test: Swipe up from app, scroll immediately, free scroll should be enabled
Test: Swipe up immediately after quick switch, task thumbnails are loaded
Change-Id: Id88266634183dfcb18d5ba8a803883b7d6f50ab4