Prevent list items being moved to inconsistent positions

[pcdavid]

Since node DnD has been added, it is possible to move all nodes to arbitrary positions, including outside of their parent.

When a node is moved only partially outside of its parent, we currently leave it there.

For rectangle/image/list nodes, this is voluntary as in such a case we want the parent to expand to include the new node's position (this will be handled as part of a more general work on node resize and overlap handling).

For list items however this never makes sense. It should be possible to DnD list items, but not to change their position inside their parent like this:

simplescreenrecorder-2023-11-08_11.23.16.mp4