WIP; add OpenApiReferencableExtensions

Author: simon-pearson-lmk

src/Microsoft.OpenApi/Extensions/OpenApiReferencableExtensions.cs

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. 
+
+using System;
+using System.Collections.Generic;
+using Microsoft.OpenApi.Interfaces;
+using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Services;
+using Microsoft.OpenApi.Validations;
+
+namespace Microsoft.OpenApi.Extensions
+{
+    /// <summary>
+    /// TODO: tmpDbg comment
+    /// </summary>
+    public static class OpenApiReferencableExtensions
+    {
+        /// <summary>
+        /// TODO: tmpDbg comment
+        /// </summary>
+        /// <param name="element">Element to validate</param>
+        /// <param name="ruleSet">Optional set of rules to use for validation</param>
+        /// <returns>An IEnumerable of errors.  This function will never return null.</returns>
+        public static IOpenApiReferenceable ResolveReference(this IOpenApiReferenceable element, string jsonPointer)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}