util: escaping object keys in util.inspect()

PR-URL: https://github.com/nodejs/node/pull/16986
Fixes: https://github.com/nodejs/node/issues/16979


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>