Add a "field" for error factories

Allows throwing the proper exception type in the constructor for throwing constructors since fields know whether they are in JSON or buffers (constructors don't)

src/main/java/slimeknights/mantle/data/loadable/ErrorFactory.java

@@ -3,6 +3,8 @@
 import com.google.gson.JsonSyntaxException;
 import io.netty.handler.codec.DecoderException;
 import io.netty.handler.codec.EncoderException;
+import slimeknights.mantle.data.loadable.field.ConstantField;
+import slimeknights.mantle.data.loadable.field.LoadableField;
 
 import java.util.function.Consumer;
 
@@ -26,6 +28,8 @@ public RuntimeException create(RuntimeException base) {
       return base;
     }
   };
+  /** Field for constructors wishing to possibly throw */
+  LoadableField<ErrorFactory,Object> FIELD = new ConstantField<>(JSON_SYNTAX_ERROR, DECODER_EXCEPTION);
 
   /** Throws an exception from the given error */
   @Override

src/main/java/slimeknights/mantle/data/loadable/field/ConstantField.java

@@ -0,0 +1,27 @@
+package slimeknights.mantle.data.loadable.field;
+
+import com.google.gson.JsonObject;
+import net.minecraft.network.FriendlyByteBuf;
+
+/** Record field that always returns the same value, used mainly to pass a different object in JSON vs buffer parsing */
+public record ConstantField<T>(T fromJson, T fromBuffer) implements LoadableField<T,Object> {
+  public ConstantField(T value) {
+    this(value, value);
+  }
+
+  @Override
+  public T get(JsonObject json) {
+    return fromJson;
+  }
+
+  @Override
+  public T decode(FriendlyByteBuf buffer) {
+    return fromBuffer;
+  }
+
+  @Override
+  public void serialize(Object parent, JsonObject json) {}
+
+  @Override
+  public void encode(FriendlyByteBuf buffer, Object parent) {}
+}