Change home dragging logic for dead zones

- If a dragged item is not over a valid drop target
then we don't highlight anything and on drop we move
it back to its original position.
- Instead of checking if the dragged item is over the
hotseat view, now we check if the item is over the hotseat
shortcuts.
- Smartspace is a dead zone

Test: drag items from different workspaces, allapps, widget
  picker etc. to all parts of the screen and verify which
  view is targeted and where the item gets dropped.
  Check on phone/foldable/tablet.
Bug: 228201267
Change-Id: I18de576ea300d58ae645e511b238e0b946b5595a