unify logic for getting element type index

Il2CppInspector.Common/Next/Metadata/Il2CppTypeDefinition.cs

@@ -1,4 +1,5 @@
 using System.Reflection;
+using VersionedSerialization;
 using VersionedSerialization.Attributes;
 
 namespace Il2CppInspector.Next.Metadata;
@@ -82,4 +83,9 @@ public partial record struct Il2CppTypeDefinition
     public uint Token { get; private set; }
 
     public readonly bool IsValid => NameIndex != 0;
+
+    public int GetEnumElementTypeIndex(StructVersion version)
+        => version >= MetadataVersions.V350
+            ? ParentIndex
+            : ElementTypeIndex;
 }