Prevents split thumbnails from flipping when entering Overview in fake seascape

Fixes a bug where the user would see the splitscreen thumbnails swap position when entering Overview from fake seascape.

The bug arose because Overview's layout in fake seascape previously respected the primary-top secondary-bottom rule for placing splitscreen thumbnails. Actually, this needs to be flipped to preserve left-right orientation: If the user sees Task A on the left, it should always be on the left no matter how they rotate their device.

Fixed by swapping thumbnail and icon positions in SeascapePagedViewHandler#setSplitTaskSwipeRect() and setSplitIconParams(). Fake seascape will now show primary thumbnail on the "bottom" of the screen and secondary on "top."

This patch also corrects a minor calculation bug affecting icon alignment.

Fixes: 221133532
Test: Manual
Change-Id: Id587cf3815e64792d758d0e352da1e1e38cb4348