Developer Guides: Model generation

[John-Development]

https://docs.fabricmc.net/develop/data-generation/block-models#custom-supplier-method this section doesnt seem to work anymore in 1.21.5, as some classes used there doesnt exist anymore. I also couldnt find any reference to why they dissapeared in the blog, therefore it might be difficut for anyone trying to use them to update their mods to that version.

The missing classes are:

• BlockStateVariant
• VariantsBlockStateSupplier