gh-89263: Add typing.get_overloads (GH-31716)

Based on suggestions by Guido van Rossum, Spencer Brown, and Alex Waygood.

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
Co-authored-by: Ken Jin <kenjin4096@gmail.com>