Removed fly-back animation after a taskbar item drop on the bubble bar

Added logic to track whether the drop target handled the app icon drop,
in order to prevent the fly-back animation in those cases.

Bug: 397459664
Flag: com.android.wm.shell.enable_create_any_bubble
Test: Manual. Drop a taskbar icon onto the bubble bar. Observe that no
fly-back animation is performed for the dropped icon.

Change-Id: If439d7280fe9f713c181531ac899ac8ad37ed481