Only allow dragging fullscreen to bubble

When bubble to fullscreen flag is on, we should only be able to drag a
fullscreen task to bubble.
Put logic for dragging a split task to bubble behind bubble anything
flag.

Bug: 404905102
Test: atest DesktopModeVisualIndicatorTest
Test: enable bubble to fullscreen flag, check that split screen can't be
  dragged to bubble
Test: enable bubble anything flag, check that when dragging a split
  task, the bubble indicator is shown
Flag: com.android.wm.shell.enable_bubble_to_fullscreen

Change-Id: I5dd747d87934a9336656e7555215709a285ce696