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

docs/HTTP3.md

@@ -15,6 +15,8 @@ QUIC libraries we are using:
 
 [quiche](https://github.com/cloudflare/quiche) - **EXPERIMENTAL**
 
+[OpenSSL 3.2+ QUIC](https://github.com/openssl/openssl) - **EXPERIMENTAL**
+
 [msh3](https://github.com/nibanks/msh3) (with [msquic](https://github.com/microsoft/msquic)) - **EXPERIMENTAL**
 
 ## Experimental
@@ -193,6 +195,40 @@ Build curl:
 
  If `make install` results in `Permission denied` error, you will need to prepend it with `sudo`.
 
+# OpenSSL version
+
+quiche QUIC support is **EXPERIMENTAL**
+
+Build OpenSSL 3.2.0
+
+     % cd ..
+     % git clone -b openssl-3.2.0 https://github.com/openssl/openssl
+     % cd openssl
+     % ./config enable-tls1_3 --prefix=<somewhere> --libdir=<somewhere>/lib
+     % make install
+
+Build nghttp3
+
+     % cd ..
+     % git clone -b v1.1.0 https://github.com/ngtcp2/nghttp3
+     % cd nghttp3
+     % autoreconf -fi
+     % ./configure --prefix=<somewhere2> --enable-lib-only
+     % make
+     % make install
+
+Build curl:
+
+     % cd ..
+     % git clone https://github.com/curl/curl
+     % cd curl
+     % autoreconf -fi
+     % ./configure --with-openssl=<somewhere> --with-openssl-quic --with-nghttp3=<somewhere2> 
+     % make
+     % make install
+
+ If `make install` results in `Permission denied` error, you will need to prepend it with `sudo`.
+
 # msh3 (msquic) version
 
 **Note**: The msquic HTTP/3 backend is immature and is not properly functional