shlex.split: allow TextIO and deprecate None

[Avasam]

Whilst working on a setuptools stubs update (namely in setuptools.command.easy_install.CommandSpec.from_param), I noticed that shlex.split didn't allow TextIO like shlex.shlex.__init__ does. And that passing None can be allowed (but deprecated) until Python 3.12.

Unless s being anything else than a str is an accidental implementation detail that should be hidden away.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[srittau]

Just a general note: TextIO isn't an ideal annotation for parameters (similar to BinaryIO and IO). Usually, a protocol is a better option. That said, as this is only forwarded, this is better than leaving it out.