added region for new errors

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -1501,6 +1501,7 @@ internal enum ErrorCode
         ERR_NamedArgumentSpecificationBeforeFixedArgumentInDynamicInvocation = 8324,
         #endregion diagnostics introduced for C# 7.2
 
+        #region diagnostics introduced for `ref readonly`, `ref ternary` and`ref-like` features in C# 7.2
         ERR_RefConditionalAndAwait = 8325,
         ERR_RefConditionalNeedsTwoRefs = 8326,
         ERR_RefConditionalDifferentTypes = 8327,
@@ -1535,5 +1536,6 @@ internal enum ErrorCode
         ERR_EscapeLocal = 8352,
         ERR_EscapeStackAlloc = 8353,
         ERR_RefReturnThis = 8354,
+        #endregion diagnostics introduced for `ref readonly`, `ref ternary` and`ref-like` features in C# 7.2
     }
 }