Modefite - Item Definition Backport

Fixes

• Fixed issue with minecraft:custom_name not behaving correctly.
  • It would always change the item model if the item is named, despite the named item being something completeley different.

Big shoutouts to rjwaslive for doing all the heavy work for the 1.20.1 port! They are a legend.

First release, see description and wiki for full list of differences to the official items definition system from 1.21.4+.

Notable features missing:

• No minecraft:special type.
• No tint source types for minecraft:model type.