A first attempt at Wireshark dissector for Binary Representation of HTTP Messages (RFC 9292)

Hi folks,

Specs are great but when it comes to trying to understand how a protocol
works, being able to demo and dissect it can be a good learning aid.

To this end, I spent a little bit if time making a dissector for
Wireshark*. This is invoked via registering a new handler for the
message/bhttp. I've opened a Merge Request on Wireshark [1], if people
would like to kick the tyres on it, I would appreciate that. If you have
pcaps from bHTTP implementations that'd be useful too.

Once I got 90% of the way through, I realised the value of this bHTTP
dissector is limited. It will truly shine once it can integrate with an
Oblivious HTTP dissector. That sadly doesnt exist yet, it requires more
work, mainly to obtain and use the keys that would let us recurse down into
messages. I've spoken to a few people about this and we have some ideas.
I'll be around at the IETF 116 hackathon in case anyone wants to chat about
that.

Cheers
Lucas

* the meta/inception here is that I also wanted to use this process to also
better understand how to write dissectors. It works but there are some
rough edges that I expect the review process to shape up. The use of QUIC
varints didn't pose much problem, I leaned heavily on the code Alexis
Lagoutte, Peter Wu and others contributed to the extant QUIC and HTTP/3
dissectors in this respect.

[1] - https://gitlab.com/wireshark/wireshark/-/merge_requests/10067