Split Architectury extensions to Fabric classes into new classes (#116)

* Split custom RemapJarTask logic into a new class

* Split a lot of logic for Arch and Quilt mod metadata into new classes

* ArchitecturyCommonJson: Fix outdated error message

* Add minimal unit tests for ACJ and QMJ

* QuiltModJson: Fix error when there are no injected interfaces

* QuiltModJsonTest: Add test for mixin configs

* QuiltModJsonTest: Move to correct package

* Add tests for creating ACJ and QMJ instances

src/main/java/dev/architectury/loom/metadata/ModMetadataFile.java

@@ -0,0 +1,12 @@
+package dev.architectury.loom.metadata;
+
+import java.util.List;
+
+import org.jetbrains.annotations.Nullable;
+
+import net.fabricmc.loom.configuration.ifaceinject.InterfaceInjectionProcessor;
+
+public interface ModMetadataFile {
+	@Nullable String getAccessWidener();
+	List<InterfaceInjectionProcessor.InjectedInterface> getInjectedInterfaces(@Nullable String modId);
+}