http3: initial support for OpenSSL 3.2 QUIC stack

- HTTP/3 for curl using OpenSSL's own QUIC stack together
  with nghttp3
- configure with `--with-openssl-quic` to enable curl to
  build this. This requires the nghttp3 library
- implementation with the following restrictions:
  * macOS has to use an unconnected UDP socket due to an
    issue in OpenSSL's datagram implementation
    See https://github.com/openssl/openssl/issues/23251
    This makes connections to non-reponsive servers hang.
  * GET requests will send the indicator that they have
    no body in a separate QUIC packet. This may result
    in processing delays or Transfer-Encodings on proxied
    requests
  * uploads that encounter blocks will use 100% cpu as
    detection of these flow control issue is not working
    (we have not figured out to pry that from OpenSSL).

Closes #12734

lib/cf-socket.c

@@ -1630,11 +1630,17 @@ static CURLcode cf_udp_setup_quic(struct Curl_cfilter *cf,
   /* QUIC needs a connected socket, nonblocking */
   DEBUGASSERT(ctx->sock != CURL_SOCKET_BAD);
 
+#if defined(__APPLE__) && defined(USE_OPENSSL_QUIC)
+  (void)rc;
+  /* On macOS OpenSSL QUIC fails on connected sockets.
+   * see: <https://github.com/openssl/openssl/issues/23251> */
+#else
   rc = connect(ctx->sock, &ctx->addr.sa_addr, ctx->addr.addrlen);
   if(-1 == rc) {
     return socket_connect_result(data, ctx->r_ip, SOCKERRNO);
   }
   ctx->sock_connected = TRUE;
+#endif
   set_local_ip(cf, data);
   CURL_TRC_CF(data, cf, "%s socket %" CURL_FORMAT_SOCKET_T
               " connected: [%s:%d] -> [%s:%d]",