tls: fix object prototype type confusion

Use `Object.create(null)` for dictionary objects so that keys from
certificate strings or the authorityInfoAccess field cannot conflict
with Object.prototype properties.

PR-URL: https://github.com/nodejs/node/pull/14447


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>