fs: improve mode and flags validation

This fixes a few bugs in `fs`. E.g., `fs.promises.access` accepted
strings as mode. It should have only accepted numbers. It will now
always validate the flags and the mode argument in an consistent way.

PR-URL: https://github.com/nodejs/node/pull/27044


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>