url: set toStringTag for the URL class

PR-URL: https://github.com/nodejs/node/pull/10562
Fixes: https://github.com/nodejs/node/issues/10554


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>