Make ACTION_CANCEL cancel drag-to-desktop

Before this CL ACTION_CANCEL wouldn't properly finish the enter-desktop
transition, making it possible to get stuck in the middle of that
transition.

Test: manual: start app-handle drag with one finger, then tap the screen
with another finger -> ensure the app goes back to fullscreen.
Bug: 373031959
Flag: EXEMPT TODO
Change-Id: Id691042d285e9a80db02fcc9fad9c3fea0fcbdfe

Change-Id: I36c811bb78ac73bf2d276c94e2af2ea6b4f2f2db