Variants-CIT

Porting to MC 1.21.4. Some Java API breaking changes, but no datapack breaking changes other than the removal of model override predicates. Most old packs should work out of the box.

• Modules now use items/ instead of models/ as primary assets.
• Modules may now automatically generate basic items assets based on existing and mod-generated models. Enabled by default for backward compatibility, can be disabled by setting itemsFromModels to false in the module.
• Item assets are searched for at the root of items/, but corresponding models and textures are now searched for in models/item/ and textures/item/. For backward compatibility, any leading "item/" will automatically be stripped off model prefixes, fallback models, and special models.
• Added the numeric property variants-cit:stored_enchantment_level, usable in item assets as a replacement for the old level model override predicate

Java API:

• Removed all deprecated methods.
• Replaced all ModelIdentifiers with plain Identifiers.