[3.13] gh-141004: Document stack effect C APIs (GH-141843) (GH-141917)

gh-141004: Document stack effect C APIs (GH-141843)
(cherry picked from commit e1f1df4082e2bc6cdb46be9984124c88a7b2ff0f)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>