Add project files.

Compat.Private.Serialization/Compat/Runtime/Serialization/DiagnosticUtility.cs

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+using System;
+using System.Diagnostics;
+
+namespace Compat.Runtime.Serialization
+{
+    internal class DiagnosticUtility
+    {
+        public class ExceptionUtility
+        {
+            internal static Exception ThrowHelperFatal(string message, Exception innerException)
+            {
+                return ThrowHelperError(new FatalException(message, innerException));
+            }
+
+            internal static Exception ThrowHelperError(Exception exception)
+            {
+                return ThrowHelper(exception, TraceEventType.Error);
+            }
+
+            internal static Exception ThrowHelper(Exception exception, TraceEventType eventType)
+            {
+                return exception;
+            }
+
+        }
+    }
+}