[3.11] [3.12] gh-112316: improve docs for `inspect.signature` and `inspect.Signature` (GH-112631) (GH-112649) (#112652)

[3.12] gh-112316: improve docs for `inspect.signature` and `inspect.Signature` (GH-112631) (GH-112649)

(cherry-picked from commit fc9e24b01fb7da4160b82cef26981d72bb678c13)
(cherry picked from commit 6221482f0c459c2e7dbd946265069246a400072a)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>