Finish drag when cancel transaction is aborted

Without this CL, in a certain case,
TRANSIT_DESKTOP_MODE_START_DRAG_TO_DESKTOP never ends after a user
completes drag operations, and the app becomes unresponsible. This CL
is to add missing cleanup.

Currently when a user starts dragging the fullscreen window handle to
freeform, then drags back to the fullscreen, there are two window
transactions involving this.

- TRANSIT_DESKTOP_MODE_START_DRAG_TO_DESKTOP starts when a user starts
  drag and ends when a user completes drag.
- TRANSIT_DESKTOP_MODE_CANCEL_DRAG_TO_DESKTOP when a user ends the drag
  after they drag back to fullscreen.

Because the later starts when the former is being played, later is
either 1) merged to former, or 2) aborted when it's noop. For the merge
case, we finishes the former transaction in the `mergeAnimation`
callback. For the abort case, it did nothing in the
`onTransitionConsumed` callback before the CL.

Bug: 370596057
Flag: EXEMPT bugfix
Test: Follow the repro step in the above bug
Change-Id: Icfc40ba8f6193bed2ded8f7095fba95b9b60aad8