Re-add the reference fields for reflection purposes.

Author: timcassell

src/BenchmarkDotNet/Engines/Consumer.cs

@@ -33,6 +33,14 @@ private static readonly HashSet<Type> SupportedTypes
         private IntPtr ptrHolder;
         private UIntPtr uptrHolder;
 
+        // We don't write to these, they are only included for reflection.
+#pragma warning disable CA1823 // Unused field
+#pragma warning disable CS0169 // The field is never used
+        private string stringHolder;
+        private object objectHolder;
+#pragma warning restore CS0169 // The field is never used
+#pragma warning restore CA1823 // Unused field
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         [PublicAPI]
         public void Consume(byte byteValue) => byteHolder = byteValue;