Fix bug in getVisualCenter where we do not offset by the dragRegion.

This bug made it hard to create folders in landscape mode because since the
visual center was off, placing the drag view directly in the center of the
cell caused the underlying item to move since the distance calculation placed
the drag view outside of the folder creation range.

Bug: 111939693
Change-Id: Id0bccb87a87ff1be188def61e697319381f725e1