Although it has better implementation status than HTTP/3 server push,
it remains of limited use, with adoption numbers seen as negligible.
Per IETF 102 materials, server push was used only in 0.04% of sessions.
It was considered to be "difficult to use effectively" in RFC 9113.
Its use is further limited by badly matching to fetch/cache/connection
models in browsers, see related discussions linked from [1].

Server push was disabled in Chrome 106 [2].

The http2_push, http2_push_preload, and http2_max_concurrent_pushes
directives are made obsolete.  In particular, this essentially reverts
7201:641306096f5b and 7207:3d2b0b02bd3d.

[1] https://jakearchibald.com/2017/h2-push-tougher-than-i-thought/
[2] https://chromestatus.com/feature/6302414934114304

The change allows to compile QUIC with OpenSSL which lacks BoringSSL QUIC API.

This implementation does not support 0-RTT.

Previously, QUIC used the existing UDP framework, which was created for UDP in
Stream.  However the way QUIC connections are created and looked up is different
from the way UDP connections in Stream are created and looked up.  Now these
two implementations are decoupled.

ngx_http_v2_huff_decode.c and ngx_http_v2_huff_encode.c are renamed
to ngx_http_huff_decode.c and ngx_http_huff_encode.c.

Renamed and removed some macros.

ngx_http_v3_tables.h and ngx_http_v3_tables.c are renamed to
ngx_http_v3_table.h and ngx_http_v3_table.c to better match HTTP/2 code.

ngx_http_v3_streams.h and ngx_http_v3_streams.c are renamed to
ngx_http_v3_uni.h and ngx_http_v3_uni.c to better match their content.