[FEATURE] Port Forgotten Graves to MC v1.20.5 & v1.20.6

[ginsm]

I've already started porting to 1.20.5 but there seems to be quite a bit of work needed (and new concepts to learn, at least for me). You can track the progress here.. but there's no ETA yet as I'm not even 100% sure what I need to learn or do. 🤣

[ginsm]

I've been looking through the codebase and it looks like I'll need to update quite a lot of it for 1.20.5 and 1.20.6. I have a better idea than I did last week on getting it up-to-date but there's definitely no ETA. I'll try and work on it here and there and hopefully it's done sooner than later.

[ginsm]

Looking through the errors, here are some things that need to be done:

• [ ] Networking needs to be swapped to using payloads.
• [ ] readNbt and writeNbt calls need access to RegistryWrapper.WrapperLookup.
• [x] World.getDimensionKey no longer exists; I'll need to figure out the alternative.
• [ ] ServerState.java has some issues with overridden methods and the Type has changed.
• [ ] ItemStack no longer has a getNbt method; used in Skull.java. I'm assuming I'll need to get a component instead.
• [ ] I need to figure out how to create GameProfiles again for the custom skulls (I was using NbtHelper.toGameProfile).

In addition, I'll need to make sure all the changes don't break previous versions within the multi-version codebase.