Close #19030: inspect.getmembers and inspect.classify_class_attrs

Close #19030: inspect.getmembers and inspect.classify_class_attrs

Order of search is now:
  1. Try getattr
  2. If that throws an exception, check __dict__ directly
  3. If still not found, walk the mro looking for the eldest class that has
     the attribute (e.g. things returned by __getattr__)
  4. If none of that works (e.g. due to a buggy __dir__, __getattr__, etc.
     method or missing __slot__ attribute), ignore the attribute entirely.