bpo-33134: dataclasses: use function dispatch table for hash, instead of a string lookup which then is tested with if tests. (GH-6222)


* Change _hash_action to be a function table lookup, instead of a list
of strings which is then tested with if statements.
(cherry picked from commit 01d618c5)
Co-authored-by: Eric V. Smith <ericvsmith@users.noreply.github.com>