Fix boat and minecart inventories on region switch

[coredex-source]

This PR fixes an inconsistency in the Craft implementations of a few entity inventory holders. While this doesn't rly do anything on Paper, it does cause issues on Folia based forks, which is how this was found. This just fixes the inconsistency furthest upstream since it just makes sense to have it up here.

Link to the original patch - CraftCanvasMC/Canvas@b04a094

[NonSwag]

Why should this be merged in Paper if it doesn't affect it?
PRing it to Folia makes more sense in this case.
Also, if the underlying inventory instance changes, wouldn't it make more sense to replace the cached version then?
This seems like potentially a lot of new redundant instances when called often.

[Dueris]

Because the inconsistency is in Paper. All other implementations of InventoryHolder also do the same thing introduced here. It made sense to merge to Paper rather than Folia because it seemed more of an inconsistency with Papers/CraftBukkits code(Idk who originally authored it whatever), rather than a bug introduced by Folia. The bug in Folia seemed more of a product of it of sorts. Just seemed easier and made more sense IMO to upstream it to Paper

[NonSwag]

Ah I see, makes sense.
Imo it would make sense to add a method contract to the API to indicate a new instance is created every time, but not sure if that is in the scope of this PR (or even wanted)…

[coredex-source]

The PR is kept very minimal to simply just make it consistent.