textproc/libxml2: update to 2.14.4

Changelog: https://gitlab.gnome.org/GNOME/libxml2/-/blob/v2.14.4/NEWS

textproc/py-libxml2 child port is moved to textproc/libxml2-python
to match the Python package name upstream specified; it now USES=python
to build after do-configure. Consumers adjusted to match.

Includes two bug-fix commits.

PR: 279705