fs: expose Stats times as Numbers

PR-URL: https://github.com/nodejs/node/pull/13173
Fixes: https://github.com/nodejs/node/issues/8276
Refs: https://github.com/nodejs/node/pull/12607
Refs: https://github.com/nodejs/node/pull/12818


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Brian White <mscdex@mscdex.net>