Add support for baking multiple models in the standalone API

[SquidDev]

The current standalone model API currently is designed around baking a single model, loaded from the resource pack. However, Minecraft's other model APIs (e.g. ItemModel.Unbaked) work differently, with consumers being responsible for marking dependencies, fetching model(s) from the bakery, and baking them.

This adds similar support to the standalone model system, with the addition of a new interface.

public interface UnbakedStandaloneModel<T> extends ResolvableModel {
    T bake(ModelBaker baker);
}

This allows mods to implement dynamic models for their modded game content, in the style of ItemModel. See this discussion on Discord for more context.

In the future it would make sense to remove the modelId from StandaloneModelKey (as it is no longer tied to a single model), and have an API closer to Fabric's (FabricMC/fabric#4565). I've not done so for now, as it felt like an unnecessary breaking change, but happy to do so now if preferred!

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

[Technici4n]

We might want to wait for model loading plugins, and see how this would fit into that system?

[SquidDev]

I would 100% be in favour of just pulling in Fabric's model loading API. However, #1884 seems incredibly WIP at this point, so it didn't feel worth pushing this back — I feel this is a fairly standalone change that we'll want either way.

[Technici4n]

LGTM!

[neoforged-releases]

🚀 This PR has been released as NeoForge version 21.5.49-beta.

[SquidDev]

Thanks all!