Port to 1.21

[embeddedt]

This PR will track porting progress to 1.21. Everything compiles and (mostly) runs, however, there are quite a few bugs and things worth noting:

• Fabric's model loading API is not updated yet so the code for that is commented out.
• The Identifier constructor became private, which resulted in a lot of new Identifier->Identifier.of refactoring.
• Enchantments now need RegistryEntry to detect whether they are a curse, etc. At the moment I just retrieve the entry from the registry at each point it's needed rather than storing the RegistryEntry.
• The stack batcher is broken by the redesign of VertexConsumerProvider.Immediate in 24w21a; rendering the first batch works but it crashes as soon as it needs to update. Cause of this is not yet known. Rendering works fine with the batcher disabled, though.
• EmiShapedRecipe.setRemainders doesn't function and throws many errors because the new recipe input system resizes the inventory to fit the given recipe, which breaks the indexing logic.
• I have most likely changed a few things you'd rather be abstracted out into EmiPort. :)

[emilyploszaj]

This PR is not going to be merged, as discussed, since you ended up being busy, I did the changes locally and will hopefully push soon. Thanks for your contribution though, I did use it to base my abstraction changes.