fs: fix functions executed in wrong context

The callback should run in the global scope and not in the FSReqWrap
context.

PR-URL: https://github.com/nodejs/node/pull/18668
Refs: https://github.com/nodejs/node/pull/12562
Refs: https://github.com/nodejs/node/pull/12976


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>