Support correctly shifting a dragged layer into an empty layer that has a Transform node

Before #2689, which removed the dummy blank `Vector` table row, we used to be able to drag an object layer into a layer with a Transform node, and it would previously counteract the Transform node's offset to prevent a shift. Now, in this particular case, it doesn't offset it.

https://github.com/user-attachments/assets/2d6d9f94-440a-44a2-988a-83ed23fa18b8

Start by reproducing the drag described in the issue: move an object layer into an empty layer containing a Transform node, comparing behavior before and after #2689. Trace the layer and Transform-node handling involved in that operation; done means the dragged layer no longer shifts when entering the empty transformed layer.

Scritto dal modello di indicizzazione a partire dal testo della issue.