Issue #25318: Optimize backslashreplace and xmlcharrefreplace error handlers in
UTF-8 encoder. Optimize also backslashreplace error handler for ASCII and
Latin1 encoders.
Use the new _PyBytesWriter API to optimize these error handlers for the
encoders. It avoids to create an exception and call the slow implementation of
the error handler.
Add a new private API to optimize Unicode encoders. It uses a small buffer
allocated on the stack and supports overallocation.
Use _PyBytesWriter API for UCS1 (ASCII and Latin1) and UTF-8 encoders. Enable
overallocation for the UTF-8 encoder with error handlers.
unicode_encode_ucs1(): initialize collend to collstart+1 to not check the
current character twice, we already know that it is not ASCII.
The utf-16* and utf-32* encoders no longer allow surrogate code points
(U+D800-U+DFFF) to be encoded.
The utf-32* decoders no longer decode byte sequences that correspond to
surrogate code points.
The surrogatepass error handler now works with the utf-16* and utf-32* codecs.
Based on patches by Victor Stinner and Kang-Hao (Kenny) Lu.
