Encrypted ClientHello (ECH)

It would be great to have support for TLS Encrypted SNI (ESNI) in Conscrypt, so Android apps can include Conscrypt to get TLSv1.3 and ESNI support. Work is already underway in boringssl and openssl to support ESNI, so it should be relatively straightforward

I'm working with others on implementing Encrypted SNI on services used on Android. ESNI is up to draft4 in the IETF process, so now is a good time to start implementing in order to provide feedback to the IETF process. We're wondering how much interest there is here in TLSv1.3 Encrypt SNI extension that is currently an IETF draft implemented by Firefox, Cloudflare, and others. We could potentially submit code to make Conscrypt support ESNI. We are currently working on getting ESNI implemented in openssl, curl, and lighttpd.