Features from rustls not yet in rustls-ffi

[jsha]

This is a tracking issue. The first link in each line is to the rustls documentation. The second link, when present, is to a rustls-ffi issue. Before working on one of these items, please file a separate issue for it (if there isn't already one), then ping this thread and I'll edit in the ticket number. We should prioritize features based on downstream projects that want to use them.

• [x] Acceptor - #155
• [x] FIPS support - https://github.com/rustls/rustls-ffi/pull/478
• [x] Client-side ECH
• [ ] Unbuffered API
• [ ] IoState
• [ ] QUIC - #100
• [ ] KxGroups
• [x] KeyLog
• [x] ClientCertVerifier
• [ ] Stream, StreamOwned
• [ ] ServerSessionMemoryCache and ClientSessionMemoryCache
• [ ] Client-side session persistence - #232
• [ ] Ticketer and ProducesTickets
• [ ] WriteEarlyData
• [ ] Parsing of certificates for custom certificate verifiers (requires additional library)
• [ ] Vectored reads (vectored writes are already done)
• [ ] Reading into uninitialized memory (requires Rust RFC implementation)

[cpu]

KeyLog

Checked-off based on https://github.com/rustls/rustls-ffi/pull/465

[cpu]

Added FIPS, client-side ECH, unbuffered APIs.