adding `itemdata` json file support for MappingGenerator

[BredyAK]

Problem Description

nope.

Solution Description

inspired from https://github.com/ViaVersion/ViaBackwards/wiki#adding-custom-model-data, but currently i could only find one way to add item custom_model_data mapping, that's extracting the existing .nbt file from ViaBackwards.jar to the plugin folder then open it in editor, and then add the custom_model_data one by one under the itemdata key, that's a little laborious, so why not make the MappingGenerator more clever?

as the image displayed, we could add a new key itemdata in diff/mapping-XXXtoXXX.json (you could consider making it support item names (like spruce_chest_boat), not only the number ids), then use the generator to output the .nbt file with itemdata. the generator could output the itemdata file with name itemdata.nbt as an individual file.

Alternatives

No response

Additional Info

No response