[3.13] gh-144148: Update the urllib.parse documentation (GH-144497) (GH-144507) (GH-144509)

(cherry picked from commit 2fb9cde118b1c5c96d9c9ce24f886d683e8c3ebb)

Document urlsplit() as the main parsing function and urlparse() as
an obsolete variant.
(cherry picked from commit 67ddba9aa9c0405c68e691643c4aa75fdbcefe1d)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>