Keep track of the minimum reliable size ACKed

Summary:
With normal resets, we transition from `StreamSendState::ResetSent` to `StreamSendState::Closed` when we get an ACK for a RESET_STREAM frame.

With reliable resets, this is going to be a little more complicated. We can't automatically transition from `StreamSendState::ResetSent` to `StreamSendState::Closed` when we get an ACK for a RESET_STREAM_AT frame because it's possible that the peer hasn't yet received all data until the reliable reset offset.

My idea is the following: Keep track of the `minReliableSizeAcked`, which is the lowest value of the reliable size in any RESET_STREAM_AT frame that was ACKed by the peer. We set it to 0 if a RESET_STREAM frame was ACKed by the peer.

Then, we can transition from `StreamSendState::ResetSent` to `StreamSendState::Closed` if any one of the following two events happen:
* We get an ACK for a RESET_STREAM_AT or a RESET_STREAM frame, and all data until the `minReliableSizeAcked` has been ACKed by the peer.
* We get an ACK for stream data, and this puts us in a state where all data until the `minReliableSizeAcked` has been ACKed by the peer.

Note: This diff doesn't have any functional change. The only change is that we're keeping track of the `minReliableSizeAcked`, but aren't using it anywhere.

Reviewed By: mjoras

Differential Revision: D66781199

fbshipit-source-id: 2aa5138a18f70e9801e59e747460558ba706939c

quic/server/state/ServerStateMachine.cpp

@@ -1060,7 +1060,7 @@ void onServerReadDataFromOpen(
                       << frame.streamId << " " << conn;
               auto stream = conn.streamManager->getStream(frame.streamId);
               if (stream) {
-                sendRstAckSMHandler(*stream);
+                sendRstAckSMHandler(*stream, frame.reliableSize);
               }
               break;
             }