Update to 1.21.4

[CringeStar]

Branch: "main"

BuiltinModelItemRenderer, ModelPredicateProviderRegistry, and EntityModelLoader are gone, so we must figure out the new rendering system.

BuiltinModelItemRenderer: It seems like this was broken up into separate classes for the items it used to handle, so the new class we have to mixin looks to be ShieldModelRenderer.

ModelPredicateProviderRegistry: Seems to be done through JSON now.

EntityModelLoader changed to LoadedEntityModels.

[CringeStar]

Entitymodelloader is all sorted, references just had to be renamed.

Predicates: Done through JSON now, they do work, currently looking for a way to make them inheritable.

Custom shield rendering: Got it to work, banner shield renders properly, but it seems hardcoded to test shield?

Track progress at: https://github.com/CringeStar/Fabric-Shield-Lib/tree/1.21.4