util: use @@toStringTag

uses @@toStringTag when creating the "tag" for an inspected value

PR-URL: https://github.com/nodejs/node/pull/16956


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>