QUIC client and server AsyncTransport wrappers

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

quic/api/test/QuicStreamAsyncTransportTest.cpp

@@ -135,6 +135,10 @@ class QuicStreamAsyncTransportTest : public Test {
   }
 
   void TearDown() override {
+    if (serverAsyncWrapper_) {
+      serverAsyncWrapper_->getEventBase()->runInEventBaseThreadAndWait(
+          [&]() { serverAsyncWrapper_.reset(); });
+    }
     server_->shutdown();
     server_ = nullptr;
     clientEvb_.runInEventBaseThreadAndWait([&] {