Summary:
Helper classes for easy experimentation with QUIC in existing code using folly::AsyncSockets, using single QUIC bidi stream.
1) QuicStreamAsyncTransport buffers writes/read callback assignment until stream id is assigned. This similar to AsyncSocket that handles connect() internally and allows consumers to read/write right away after instance creation.
2) Quic(Client|Server)AsyncTransport handle connection level callbacks and update stream id on corresponding stream event
3) QuicAsyncTransportAcceptor and QuicAsyncTransportServer handle wangle::ManagedConnections, which are commonly used with folly::AsyncServerSockets
Reviewed By: yangchi
Differential Revision: D24656620
fbshipit-source-id: 75f9eb66c6cc8b7b1b974912d760c8aae5a5809f
