Item duplication with chested donkeys, mules and llamas

To reproduce

1. Spawn in a donkey, tame it, and equip it with a chest
2. Player 2 opens the donkey's inventory
3. Player 2 places items to duplicate in the inventory and keeps the GUI open
4. Player 1 mounts the chested horse/donkey
5. Player 1 disconnects, the donkey disappears
   → Player 2's GUI stays open
6. Player 2 grabs items from the inventory
7. Player 1 logs back in, along with the donkey
   → The donkey still has the items in its inventory, thus the items have been duplicated

Credit

This issue was originally reported on Paper's GH here: https://github.com/PaperMC/Paper/issues/2580

Video

The video in the report: https://www.youtube.com/watch?v=HIn_d_nbceY

I've forwarded the issue here since I do not know if it's been reported already.

Suggested fix

Close the inventory when the entity (chested animal) is removed from the world.