Stair ledges cause items to move to the nearest free space

Items thrown on stair ledges make them move to the nearest free horizontal position.

Steps to Reproduce

1. Obtain any stair
2. Obtain any item
3. Place the stair
4. Throw the item on it

Here, the item will bounce backwards towards the player.

Video Example

https://youtu.be/rjZE5JG2khU