[Node.Fs] add `accessSync` and `copyFileSync` bindings, along with `Fs.Constants` module

[mrvicadai]

Summary

• [x] Replace nodeFs.ml with nodeFs.re. (This one might be controversial -- so I'm expecting pushbacks here)
  • Most folks who try to use NodeJS are going to use ReasonML syntax -- this makes the binding more legible and approachable.
  • ReasonML comes battery-included with refmt, which makes the formatting consistent.
• [x] Add accessSync binding to Node.Fs.
• [x] Add copyFileSync binding to Node.Fs.
• [x] Add Fs.Constants module: https://nodejs.org/api/fs.html#fs_fs_constants_1