common,server: handle bracketed IPv6 literals in URL authority (#25140)

common,server: handle bracketed IPv6 literals in URL authority (#25140)

* common,server: handle bracketed IPv6 literals in URL authority

Parse the [host]:port form (RFC 3986) and bracket IPv6 hosts when
formatting a URL authority: listening log, proxy Host header, proxy
log, client rebuild. The per-request remote_addr stays bare.

* common: restore unsupported scheme throw in url parser

Address @ngxson review: keep the explicit reject in port resolution so
the block stays self-contained. Non-http(s) schemes still throw (also
gated at the top of common_http_parse_url).