Docs: Reword inline docs for better readability and clarity.

This improves the wording of the inline documentation for `redirect_guess_404_permalink()` and the related filters introduced in [47878].

Previously [47878,47885]
See #16557.
Built from https://develop.svn.wordpress.org/trunk@48182


git-svn-id: https://core.svn.wordpress.org/trunk@47951 1a063a9b-81f0-0310-95a4-ce76da25c4cd