Fix dependency loop and improve namings

Summary:
Fixing dependency loop introduced by D37799050 (96abc8160d)

Running `autodeps` yields the following patch:

```
 --- a/xplat/quic/state/TARGETS
+++ b/xplat/quic/state/TARGETS
@@ -43,8 +43,8 @@
     exported_deps = [
         "//folly:random",
         "//quic:constants",
+        "//quic/codec:codec",
         "//quic/codec:types",
-        "//quic/common:circular_deque",
         "//quic/common:interval_set",
     ],
 )
```

If this patch is applied, there is a circular dependency loop between `//quic/codec:codec` and `//quic/state:ack_states` by way of `//quic/codec:types`; this loop was introduced by D37799050 (96abc8160d).

Fixed by separating out headers files and targets. In parallel, renamed structures used for writing ACK frames (which were the reason this loop occurred) to make their role clear.

Differential Revision: D42281359

fbshipit-source-id: 8514c99f3fe72ff1d942d7f303e4a209838c7623

quic/api/QuicPacketScheduler.cpp

@@ -586,7 +586,7 @@ folly::Optional<PacketNum> AckScheduler::writeNextAcks(
                  ackingTime - receivedTime)
            : 0us);
 
-  AckFrameMetaData meta = {
+  WriteAckFrameMetaData meta = {
       ackState_, /* ackState*/
       ackDelay, /* ackDelay */
       static_cast<uint8_t>(ackDelayExponentToUse), /* ackDelayExponent */
@@ -594,7 +594,7 @@ folly::Optional<PacketNum> AckScheduler::writeNextAcks(
       folly::none, /* recvTimestampsConfig */
       folly::none /* maxAckReceiveTimestampsToSend */};
 
-  folly::Optional<AckFrameWriteResult> ackWriteResult;
+  folly::Optional<WriteAckFrameResult> ackWriteResult;
 
   bool isAckReceiveTimestampsSupported =
       conn_.transportSettings.maybeAckReceiveTimestampsConfigSentToPeer &&