clean up TypeDefinitionConverter code

AssetStudioUtility/Unity.CecilTools/Extensions/ResolutionExtensions.cs

@@ -0,0 +1,36 @@
+// Unity C# reference source
+// Copyright (c) Unity Technologies. For terms of use, see
+// https://unity3d.com/legal/licenses/Unity_Reference_Only_License
+
+using System;
+using Mono.Cecil;
+
+namespace Unity.CecilTools.Extensions
+{
+    public static class ResolutionExtensions
+    {
+        public static TypeDefinition CheckedResolve(this TypeReference type)
+        {
+            return Resolve(type, reference => reference.Resolve());
+        }
+
+        public static MethodDefinition CheckedResolve(this MethodReference method)
+        {
+            return Resolve(method, reference => reference.Resolve());
+        }
+
+        private static TDefinition Resolve<TReference, TDefinition>(TReference reference, Func<TReference, TDefinition> resolve)
+            where TReference : MemberReference
+            where TDefinition : class, IMemberDefinition
+        {
+            if (reference.Module == null)
+                throw new ResolutionException(reference);
+
+            var definition = resolve(reference);
+            if (definition == null)
+                throw new ResolutionException(reference);
+
+            return definition;
+        }
+    }
+}