Make the AckState for Initial/Handshake a unique_ptr

Summary:
We don't need to carry these states after the handshake is confirmed, so make them pointers instead. This will facilitate adding a structure to the AckState for tracking duplicate packets.

(Note: this ignores all push blocking failures!)

Reviewed By: hanidamlaj

Differential Revision: D41626895

fbshipit-source-id: d8ac960b3672b9bb9adaaececa53a1203ec801e0

quic/api/test/QuicTransportBaseTest.cpp

@@ -841,7 +841,7 @@ TEST_P(QuicTransportImplTestBase, WriteAckPacketUnsetsLooper) {
       pktHasCryptoData,
       Clock::now());
   ASSERT_TRUE(transport->transportConn->ackStates.initialAckState
-                  .needsToSendAckImmediately);
+                  ->needsToSendAckImmediately);
   // Trigger the loop callback. This will trigger writes and we assume this will
   // write the acks since we have nothing else to write.
   transport->writeLooper()->runLoopCallback();