Add logic to show the expanded view drop target.

Added logic to show the expanded view silhouette at the Bubble Bar drop
location.

Bug: 388894910
Flag: com.android.wm.shell.enable_create_any_bubble
Test: Manual. Drag an app icon from the taskbar while inside the
application. Observe the expanded view appearing when the icon is
dragged over the Bubble Bar location and disappearing when dragged out.
video: http://recall/-/gx8ASgewUeUS3QYohfrd1J/erIYLNwEjzD0T5konPIdY6

Change-Id: I75433972c761fc6e99e46d999a2975131346e90f