gh-92345: Import rlcompleter before sys.path is extended (#92346)

``pymain_run_python()`` now imports ``readline`` and ``rlcompleter``
before sys.path is extended to include the current working directory of
an interactive interpreter. Non-interactive interpreters are not
affected.

Also move imports of ``re`` and ``keyword`` module to top level so they
are materialized early, too. The ``keyword`` module is trivial and the
``re`` is already imported via ``inspect`` -> ``linecache``.