fs: add *timeNs properties to BigInt Stats objects

- Extend the aliased buffer for stats objects to contain
  the entire time spec (seconds and nanoseconds) for the time
  values instead of calculating the milliseconds in C++ and
  lose precision there.
- Calculate the nanosecond-precision time values in JS and expose
  them in BigInt Stats objects as `*timeNs`. The
  millisecond-precision values are now calculated from the
  nanosecond-precision values.

PR-URL: https://github.com/nodejs/node/pull/21387


Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>