feat(resourcemanager): add TypeReferenceTypeAttribute (#26127)

Add an attribute which can be used to mark `x-ms-mgmt-typeReferenceType`

part of Azure/autorest.csharp#1761

sdk/resourcemanager/Azure.ResourceManager/src/Internal/TypeReferenceTypeAttribute.cs

@@ -0,0 +1,15 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System;
+
+namespace Azure.ResourceManager.Core
+{
+    /// <summary>
+    /// An attribute class indicating a reference type which can replace a type in target RPs.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class)]
+    internal class TypeReferenceTypeAttribute : Attribute
+    {
+    }
+}