add new struct definitions

Il2CppInspector.Common/Next/Metadata/Il2CppFieldRef.cs

@@ -0,0 +1,13 @@
+using VersionedSerialization.Attributes;
+
+namespace Il2CppInspector.Next.Metadata;
+
+using FieldIndex = int;
+using TypeIndex = int;
+
+[VersionedStruct]
+public partial struct Il2CppFieldRef
+{
+    public TypeIndex TypeIndex { get; private set; }
+    public FieldIndex FieldIndex { get; private set; }
+}