Check if types are not annotated with `preferred_name`

[aaronj0]

We should be able to deduce when types have the preferred_name attribute, useful in correctly determining if we should Pythonize it or not. Currently we seed gIteratorTypes from begin()'s canonical return type (GetTypeAsString(GetCanonicalType(...))) but look it up by the iterator's scoped-final-name (GetQualifiedCompleteName), which disagree on Apple's libc++