Update visuals of drop target

- 2dp as per VisD
- color should be primary fixed
- I bumped the elevation above 1dp so that it would be above the dismiss
  target in launcher / above the scrim that shows with the drop target.
- Had to bump elevation of dragged views to stay above the drop target.

Flag: com.android.wm.shell.enable_bubble_anything
Test: manual / visual - drag a bubble or drag expanded view and observe
                        the drop targets
Bug: 403276099
Change-Id: Iaec895d7ec489b6eada1e9b0114961eff8f27834