fs: improve errors in watchFile and unwatchFile

- Check if the watcher is active in JS land before
  invoking the binding, act as a noop if the state of
  the watcher does not match the expectation. This
  avoids firing 'stop' when the watcher is already
  stopped.
- Update comments, validate more arguments and
  the type of the handle.
- Handle the errors from uv_fs_poll_start
- Create an `IsActive` helper method on StatWatcher

PR-URL: https://github.com/nodejs/node/pull/19345
Refs: https://github.com/nodejs/node/pull/19089


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>