src,http2: introduce node_http_common

The nghttp2 and nghttp3 (used in the QUIC implementation) share nearly
identical structs for header handling. However, they differ enough that
they need to be handled slightly different in each case. This PR
includes some elements introduced in the QUIC PR separated out to
make them independently reviewable, and updates the http2 implementation
to use the shared utilities.

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/32069


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>