=> we want to use the extremum of finger location and object
center for snapping to a new screen (max when snapping to right,
min when snapping to left)
=> when selecting a panel within the current screen, we want to
rely strictly on the object center to determine selection; there
is plenty of space to be consistent here, and extremum logic
could cause thrashing back and forth with no page movement.
Test: Manual. See videos in b/221104663. On two-panel and one-panel
test dragging a widget between different screens with
different starting positions of where the widget goes down.
Bug 221104663
Change-Id: I8f0f13f07b753752087a90c4bacb76cfbf7aa5bf
f2f302bcf6