The codecs lookup function now performs only minimal normalization of
the encoding name before passing it to the search functions:
all ASCII letters are converted to lower case, spaces are replaced
with hyphens.

Excessive normalization broke third-party codecs providers, like
python-iconv.

Revert "bpo-37751: Fix codecs.lookup() normalization (GH-15092)"

This reverts commit 20f59fe1f7748ae899aceee4cb560e5e1f528a1f.

Add `FT_MUTEX_LOCK`/`FT_MUTEX_UNLOCK`, which call `PyMutex_Lock` and `PyMutex_Unlock` on the free-threaded build, and no-op otherwise. 

Fix name of the Python encoding in Unicode errors of the code page
codec: use "cp65000" and "cp65001" instead of "CP_UTF7" and "CP_UTF8"
which are not valid Python code names.

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

The logic of `PyCodec_BackslashReplaceErrors` is now split into separate functions,
each of which handling a specific exception type.

Writing the decimal representation of a Unicode codepoint only requires to know the number of digits.

---------

Co-authored-by: Petr Viktorin <encukou@gmail.com>