Added missing using and updated publicAPI

Author: darrelmiller

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -958,6 +958,19 @@ namespace Microsoft.OpenApi.Services
         public OpenApiReferenceError(Microsoft.OpenApi.Exceptions.OpenApiException exception) { }
         public OpenApiReferenceError(Microsoft.OpenApi.Models.OpenApiReference reference, string message) { }
     }
+    public class OpenApiUrlTreeNode
+    {
+        public System.Collections.Generic.IDictionary<string, Microsoft.OpenApi.Services.OpenApiUrlTreeNode> Children { get; }
+        public bool IsParameter { get; }
+        public string Label { get; }
+        public string Path { get; }
+        public Microsoft.OpenApi.Models.OpenApiPathItem PathItem { get; }
+        public string Segment { get; }
+        public void Attach(Microsoft.OpenApi.Models.OpenApiDocument doc, string label) { }
+        public Microsoft.OpenApi.Services.OpenApiUrlTreeNode Attach(string path, Microsoft.OpenApi.Models.OpenApiPathItem pathItem, string label) { }
+        public bool HasOperations() { }
+        public static Microsoft.OpenApi.Services.OpenApiUrlTreeNode Create(Microsoft.OpenApi.Models.OpenApiDocument doc = null, string label = "") { }
+    }
     public abstract class OpenApiVisitorBase
     {
         protected OpenApiVisitorBase() { }

test/Microsoft.OpenApi.Tests/Services/OpenApiUrlTreeNodeTests.cs

@@ -1,6 +1,11 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
+using System.Collections.Generic;
+using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Services;
+using Xunit;
+
 namespace Microsoft.OpenApi.Tests.Services
 {
     public class OpenApiUrlTreeNodeTests