Even though it cannot fall-back to a lower HTTP version automatically. The
safer way to upgrade remains via CURLOPT_ALTSVC.
CURLOPT_H3 no longer has any bits that do anything and might be removed
before we remove the experimental label.
Updated the curl tool accordingly to use "--http3".
Closes#4197
USe configure --with-ngtcp2 or --with-quiche
Using either option will enable a HTTP3 build.
Co-authored-by: Alessandro Ghedini <alessandro@ghedini.me>
Closes#3500