Fix taskbar drag view scale when returning to original icon

- Use getSourceVisualDragBounds() if the target view is BubbleTextView;
  this accounts for padding as well as extra ring inset for
  PredictedAppIcon
- Also ensure we always use the final drag view scale when switching to
  the system drag and drop, instead of using the current scale which
  might be in the process of animating

Test: drag regular and predicted icons in taskbar, but drop it in a
region that doesn't accept it (e.g. the taskbar itself), check that the
return animation scales and offsets more correctly than before
Bug: 269814838

Change-Id: Ie8398b2617340e1d2568773563aa0263a3366940