x509: allow SAN URIs to contain userinfo

x509: allow SAN URIs to contain userinfo

The way we're currently handling SAN URIs does not allow for userinfo,
meaning the name constraint check on such URIs will fail. Fix this by
skipping over the userinfo component:

      authority   = [ userinfo "@" ] host [ ":" port ]

(per RFC 3986).

Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25861)