* stdlib/xml/sax: Type annotations for commonly used methods.
* stdlib/xml/sax: More annotations.
It turns out SAX's definition of a "qname" is exactly the opposite of
ElementTree's. With that understanding, let's annotate the Attributes*Impl
classes too.
* stdlib/xml/sax: I better understand what AttributesNSImpl is doing now.
* Update third-party library stubs to agree with the new SAX annotations.
