fs: include more fs.stat*() optimizations

Including:

* Move async *stat() functions to FillStatsArray() now used by the
sync *stat() functions

* Avoid creating fs.Stats instances for implicit async/sync *stat()
calls used in various fs functions

* Store reference to Float64Array data on C++ side for easier/faster
access, instead of passing from JS to C++ on every async/sync *stat()
call

PR-URL: https://github.com/nodejs/node/pull/11665


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>