onPointerCaptureCancelled
Cancels one unfinished captured gesture on the owning tree thread.
The runtime has already removed its capture reference before this callback runs and invokes it before this node is disposed. This notification is not a synthetic release and must not assume that a pointer remains inside the node.
Parameters
button
the button whose consumed press began the cancelled gesture.
Throws
when application cancellation fails; the original failure remains primary unless an earlier failure already exists, and remaining cleanup is still attempted.