Creating a "builds" dimension

[Ghoulboy78]

This was an old idea I had when dimension API was first added. Now I know that nowadays dimension API has been a bit wonky, but basically the idea is that each player has their own dimension in which they can go and build stuff, before coming back into regular world or something like that to build normally. This way, player could also be given creative mode in their pocket dimension, and we save their inventory and then restore it when switching dimensions.