Call directly PyUnicode_DecodeUTF8Stateful() instead of PyUnicode_DecodeUTF8()
Call directly PyUnicode_DecodeUTF8Stateful() instead of PyUnicode_DecodeUTF8()

 * Remove micro-optimization from PyUnicode_FromStringAndSize():
   PyUnicode_DecodeUTF8Stateful() has already these optimizations (for size=0
   and one ascii char).
 * Rename utf8_max_char_size_and_char_count() to utf8_scanner(), and remove an
   useless variable

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator