Add dns_lookup to stdlib. Ticket #21305

*Examples:*

          dns_lookup(['1.2.3.4','example.com'])

  Returns: ['1.2.3.4','192.0.43.10']

          dns_lookup('1.2.3.4/32','i-dont-exist-domain.com')

  Returns: ['1.2.3.4/32','i-dont-exist-domain.com']