[CSharp] Enable access order checking tests.

Having ported the implementation from Java and fixed some issues where
the C# codecs were not checking the acting version when decoding data,
the tests now pass.

csharp/sbe-tests/FieldAccessOrderCheckTests.cs

@@ -8,7 +8,7 @@
 
 namespace Org.SbeTool.Sbe.Tests
 {
-    [TestClass, Ignore]
+    [TestClass]
     public class FieldAccessOrderCheckTests
     {
         private const int Offset = 0;