Fix for shell-handled drag interruption.

When a drag was handled in the shell, the DragLayout.hide() method
called the DragToBubbleController.onDragEnded() method, which ended drop
target management.

This change introduces hideDropTargets() methods to properly hide the
drop targets without ending drag handling.

Fixes: 427297270
Test: DragToBubbleControllerTest
Flag: com.android.wm.shell.enable_create_any_bubble
Change-Id: I88a1b67b72682b8ba948f95d1eaf3107f2cd5810