feat(cdk/drag-drop): allow drag to be canceled after dragged over list

### Feature Description

Items actively dragged from one list to another, but without releasing the drag, cannot be canceled. The list changes immediately and the user cannot undo the action. This issue tracks the request to enable an API that lets dragging be canceled, e.g. by undo'ing the list changes (or not change the lists at all) if the item is not dropped onto a drop container

### Use Case

_No response_

The issue names no files or tests, so start by locating the CDK drag-drop implementation and its existing drag/drop API. Compare list updates when an item is dragged over another list with the behavior when it is not dropped, then clarify the cancellation contract. Done means canceled drags do not leave unintended list changes and the API behavior is covered by tests.

Written by the indexing model from the issue text.