HTTPS eyeballing for --http3 mode.

[icing]

New cfilter HTTP-CONNECT for h3/h2/http1.1 eyeballing.

• filter is installed when --http3 in the tool is used (or the equivalent CURLOPT_ done in the library)
• starts a QUIC/HTTP/3 connect right away. Should that not succeed after 100ms (subject to change), a parallel attempt is started for HTTP/2 and HTTP/1.1 via TCP
• both attempts are subject to IPv6/IPv4 eyeballing, same as happens for other connections
• tie timeout to the ip-version HAPPY_EYEBALLS_TIMEOUT
• use a soft timeout at half the value. When the soft timeout expires, the HTTPS-CONNECT filter checks if the QUIC filter has received any data from the server. If not, it will start the HTTP/2 attempt.

HTTP/3(ngtcp2) improvements.

• setting call_data in all cfilter calls similar to http/2 and vtls filters for use in callback where no stream data is available.
• returning CURLE_PARTIAL_FILE for prematurely terminated transfers
• enabling pytest test_05 for h3
• shifting functionality to "connect" UDP sockets from ngtcp2 implementation into the udp socket cfilter. Because unconnected UDP sockets are weird. For example they error when adding to a pollset.

HTTP/3(quiche) improvements.

• fixed upload bug in quiche implementation, now passes 251 and pytest
• error codes on stream RESET
• improved debug logs
• handling of DRAIN during connect
• limiting pending event queue

HTTP/2 cfilter improvements.

• use LOG_CF macros for dynamic logging in debug build
• fix CURLcode on RST streams to be CURLE_PARTIAL_FILE
• enable pytest test_05 for h2

GOAWAY handling for ngtcp2/quiche

• during connect, when the remote server refuses to accept new connections and closes immediately (so the local conn goes into DRAIN phase), the connection is torn down and a another attempt is made after a short grace period. This is the behaviour observed with nghttpx when we tell it to shut down gracefully. Tested in pytest test_03_02.

TLS improvements

• ALPN selection for SSL/SSL-PROXY filters in one vtls set of functions, replaces copy of logic in all tls backends.

• standardized the infof logging of offered ALPNs

• ALPN negotiated: have common function for all backends that sets alpn proprty and connection related things based on the negotiated protocol (or lack thereof).

• new tests/tests-httpd/scorecard.py for testing h3/h2 protocol implementation. Invoke: python3 tests/tests-httpd/scorecard.py --help for usage.

Improvements on gathering connect statistics and socket access.

• new CF_CTRL_CONN_REPORT_STATS cfilter control for having cfilters report connection statistics. This is triggered when the connection has completely connected.
• new void Curl_pgrsTimeWas(..) method to report a timer update with a timestamp of when it happend. This allows for updating timers "later", e.g. a connect statistic after full connectivity has been reached.
• in case of HTTP eyeballing, the previous changes will update statistics only from the filter chain that "won" the eyeballing.
• new cfilter query CF_QUERY_SOCKET for retrieving the socket used by a filter chain. Added methods Curl_conn_cf_get_socket() and Curl_conn_get_socket() for convenient use of this query.
• Change VTLS backend to query their sub-filters for the socket when checks during the handshake are made.

HTTP/3 documentation on how https eyeballing works.

TLS improvements

• ALPN selection for SSL/SSL-PROXY filters in one vtls set of functions, replaces copy of logic in all tls backends.
• standardized the infof logging of offered ALPNs
• ALPN negotiated: have common function for all backends that sets alpn proprty and connection related things based on the negotiated protocol (or lack thereof).

[icing]

rebased to current with macos ci fix.

[bagder]

Thanks, another monster-PR landed.