[3.12] gh-115937: Remove implementation details from inspect.signature() docs (GH-116086) (#116106)

gh-115937: Remove implementation details from inspect.signature() docs (GH-116086)
(cherry picked from commit fb2e17b642fc3089e4f98e4bf6b09dd362e6b27d)

Co-authored-by: Erlend E. Aasland <erlend@python.org>
Co-authored-by: Carol Willing <carolcode@willingconsulting.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>