[3.13] gh-141004: Document `PyFile_OpenCode` and `PyFile_OpenCodeObject` (GH-141413) (GH-141426)

gh-141004: Document `PyFile_OpenCode` and `PyFile_OpenCodeObject` (GH-141413)
(cherry picked from commit 2befce86e699fdbb6610949b029bad56a0d0780f)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>