Trim Material incompatible_armor_material does not support modded armor materials

(This is a modding-related issue; all references to code will be using the official Mojang mapping set.)

At the moment, the incompatible_armor_material field of trim materials only supports vanilla armor materials stored in the ArmorMaterials enum and not the general ArmorMaterial interface. While this is understandably because of serialization limitations around arbitrary unregistered materials, it definitely causes an issue for mods that would want to add armor in the other standard trim materials. It feels like this should either be fixed (likely through a registry for armor materials) or documented as a limitation of the incompatible_armor_material field.