[ech] looking for comments on my current APIs for ECH

[Salz, Rich]

I won't be able to look at this until later in the month.

Can you get folks from the major forks to participate? I'd reach out to David Benjamin and Bob Beck and see if they're interested or can make a recommendation. Speaking for QuicTLS (which apparently isn't considered a major fork:) we'll just pick up whatever OpenSSL does.  But it would be great if OpenSSL, BoringSSL, and LibreSSL could agree.