[3.13] pythongh-141004: Document Py_hexdigits (pythonGH-141059) (pythonGH-141139)

pythongh-141004: Document `Py_hexdigits` (pythonGH-141059)
(cherry picked from commit 54110e2)

Co-authored-by: Stan Ulbrych <[email protected]>
Co-authored-by: Victor Stinner <[email protected]>

Author: 3 people

Doc/c-api/codec.rst

@@ -129,3 +129,13 @@ Registry API for Unicode encoding error handlers
    Replace the unicode encode error with ``\N{...}`` escapes.
 
    .. versionadded:: 3.5
+
+
+Codec utility variables
+-----------------------
+
+.. c:var:: const char *Py_hexdigits
+
+   A string constant containing the lowercase hexadecimal digits: ``"0123456789abcdef"``.
+
+   .. versionadded:: 3.3