src,lib: prefer internal/options over process._foo

This addresses a couple `TODO` comments and allows us
to remove a number of underscored properties from `process`
(in a semver-major follow-up).

PR-URL: https://github.com/nodejs/node/pull/25063


Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>