Couple fixes for drag and drop

- Add simple fade of the drag surface when dropping and when canceling a
  drag from the shade (since the shade has closed, the default animation
  of animating to the start position is wrong)
- Add case for dragging over home/recents, show the highlighted drop zone
  as fullscreen since there is nothing to split with
- Fix issue with drag listener not being removed after a notification
  drag
- For now, add a toast when attempting to drag a notification that does
  not have a valid intent
- Also don't wait for DRAG_START to start collapsing the shade if the
  call to startDrag() returns true

Bug: 217972792
Bug: 218791595
Bug: 219757067
Test: atest WMShellUnitTests
Test: atest SystemUITests

Change-Id: Ic53de0d8a999d4ae39dc207bfc2927466ad2ba7c