(MODULES-4485) Improve ipv6 support for type

[petems]

• Improves regex to catch some valid (but less
  known) ipv6 strings, mostly those which are a mix
  of ipv6 strings and embedded ipv4 numbers
• Regex inspired by the following:
  • https://github.com/sindresorhus/ip-regex
  • https://gist.github.com/cpetschnig/294476
  • The original Dartware forum thread where
    someone originally created this beast of a regex,
    now lost except to archive.org
• Whilst we're here, we can add the more tricky
  ipv6 strings to the existing functions to validate
• Luckily, the ipaddr native ruby library used
  in the original functions already supports these