fs: support Uint8Array input to methods

Allow `fs.read`, `fs.write` and `fs.writeFile` to take
`Uint8Array` arguments.

PR-URL: https://github.com/nodejs/node/pull/10382


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>