[1/n] Update desktop task drag listeners to not update task position immediately on drag stop

Before, the DragPositioningCallback would immediately send a WCT to update the task position onDragPositioningEnd. This isn't necessary all the time, since the callers of DragPositioningCallback also end up creating a WCT to set task position after their own transformations (i.e. the differnt indicator listeners in DesktopTasksController). So now, only the task leash will be updated in onDragPositiongMove, and the last position of the task leash will be returned from onDragPositioningEnd, meaning only one WCT will be needed (if needed at all).

Bug: 354280814
Flag: EXEMPT bugfix
Test: atest DesktopTasksControllerTest
Test: atest DesktopModeWindowDecorViewModelTests
Change-Id: I92fb73eff79f5c9859e7606d7a6fa21779648214