Catch and handle NRefactory parser exceptions (#6392)

Co-authored-by: vlad-andreev <[email protected]>

Author: vlad-andreev

com.unity.render-pipelines.core/Editor/ShaderGenerator/CSharpToHLSL.cs

@@ -201,7 +201,16 @@ static void LoadTypes(string fileName)
                 }*/
                 parser.Lexer.EvaluateConditionalCompilation = true;
 
-                parser.Parse();
+                try
+                {
+                    parser.Parse();
+                }
+                catch
+                {
+                    Debug.LogWarning($"Unable to parse {fileName}.  Please not that C# 6.0 syntax is not yet supported by this tool.");
+                    return;
+                }
+
                 try
                 {
                     var visitor = new NamespaceVisitor();