Add project files.

Compat.Private.Serialization/Compat/Runtime/Serialization/ExtensionDataMember.cs

@@ -0,0 +1,13 @@
+namespace Compat.Runtime.Serialization
+{
+    internal class ExtensionDataMember
+    {
+        public string Name { get; set; }
+
+        public string Namespace { get; set; }
+
+        public IDataNode Value { get; set; }
+
+        public int MemberIndex { get; set; }
+    }
+}