SVCB: Correctly parse and print unknown params

SVCB: Correctly parse and print unknown params

There were multiple issues. With this commit, we *always* store the
bytes that are represented by the option. To do this, we needed to
properly parse RFC 1035 character-strings. This is now done with a
conversion of the ABNF from draft-ietf-dnsop-svcb-https-02 to ragel.

The resulting function could be used as a starting point for a better
TXT storage format.

Fixes #9829