doc: add WHATWG file URLs in fs module

Update fs module documentation adding WHATWG file URLS support for
relevant fs functions/classes.

PR-URL: https://github.com/nodejs/node/pull/12670
Fixes: https://github.com/nodejs/node/issues/12341
Ref: https://github.com/nodejs/node/pull/10739


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>