Add project files.

Compat.Private.Serialization/CodeObject.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections;
+using System.Collections.Specialized;
+
+#if !FEATURE_SERIALIZATION
+namespace System.CodeDom
+#else
+namespace Compat.Runtime.Serialization
+#endif
+{
+#if !FEATURE_SERIALIZATION
+    public class CodeObject
+#else
+    internal class CodeObject
+#endif
+    {
+        private IDictionary _userData = null;
+
+        public CodeObject() { }
+
+        public IDictionary UserData => _userData ?? (_userData = new ListDictionary());
+    }
+}