util: mark iterator entries as such

It is possible to distinguish the entries iterator from others.
Expose that information to the users as well and improve the
Symbol.toStringTag handling by adding a special tag instead of
replacing the existent information.

PR-URL: https://github.com/nodejs/node/pull/26222


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