Snap to relative position to snappd task when dismissing

- Calculate the diff to snapped page scroll and apply in onLayout, so tasks won't jump after dismiss when not in snapped position
- In grid, always keep the relateive snapped page unchanged to avoid jump

Bug: 188793333
Test: manual
Change-Id: Id11c2d700dc55440de39cc7409d06a712cedc9bc
2 files changed