getWslDrivesMountPoint always returns "/mnt/"

[mingzz]

Function getWslDrivesMountPoint always returns the default mount point '/mnt/'. This is due to that fs.constants.F_OK always triggers the exception:

TypeError: Cannot read property 'F_OK' of undefined

According to the documentation of fs, fs.promises does not have constants. So we should probably import constants as well.

[mingzz]

Maybe due to nodejs version. The one I had was node v12.18.2.
fs.promises only has the following properties in node v14 as well:

> const { promises } = require("fs");
undefined
> promises
{
  access: [AsyncFunction: access],
  copyFile: [AsyncFunction: copyFile],
  open: [AsyncFunction: open],
  opendir: [Function: opendir],
  rename: [AsyncFunction: rename],
  truncate: [AsyncFunction: truncate],
  rmdir: [AsyncFunction: rmdir],
  mkdir: [AsyncFunction: mkdir],
  readdir: [AsyncFunction: readdir],
  readlink: [AsyncFunction: readlink],
  symlink: [AsyncFunction: symlink],
  lstat: [AsyncFunction: lstat],
  stat: [AsyncFunction: stat],
  link: [AsyncFunction: link],
  unlink: [AsyncFunction: unlink],
  chmod: [AsyncFunction: chmod],
  lchmod: [AsyncFunction: lchmod],
  lchown: [AsyncFunction: lchown],
  chown: [AsyncFunction: chown],
  utimes: [AsyncFunction: utimes],
  lutimes: [AsyncFunction: lutimes],
  realpath: [AsyncFunction: realpath],
  mkdtemp: [AsyncFunction: mkdtemp],
  writeFile: [AsyncFunction: writeFile],
  appendFile: [AsyncFunction: appendFile],
  readFile: [AsyncFunction: readFile]
}