message: Use F14ValueMap in DetailsPerStream
  Summary: This thing is fairly hot and benefits from being denser than the vector map which gets automatically selected by F14FastMap.
diff: @@ -56,7 +56,7 @@ struct OutstandingPacketMetadata {
  folly::Optional<uint64_t> maybeFirstNewStreamByteOffset;
  };
  - class DetailsPerStream : private folly::F14FastMap<StreamId, StreamDetails> {
  + class DetailsPerStream : private folly::F14ValueMap<StreamId, StreamDetails> {
  public:
  void addFrame(const WriteStreamFrame& frame, const bool newData) {
  auto ret = emplace(
  @@ -86,7 +86,7 @@ struct OutstandingPacketMetadata {
  }
  [[nodiscard]] auto at(StreamId id) const {
  - return folly::F14FastMap<StreamId, StreamDetails>::at(id);
  + return folly::F14ValueMap<StreamId, StreamDetails>::at(id);
  }
  [[nodiscard]] auto begin() const {
  @@ -97,14 +97,14 @@ struct OutstandingPacketMetadata {
  return cend();
  }
  - using folly::F14FastMap<StreamId, StreamDetails>::cbegin;
  - using folly::F14FastMap<StreamId, StreamDetails>::cend;
  - using folly::F14FastMap<StreamId, StreamDetails>::const_iterator;
  - using folly::F14FastMap<StreamId, StreamDetails>::empty;
  - using folly::F14FastMap<StreamId, StreamDetails>::find;
  - using folly::F14FastMap<StreamId, StreamDetails>::mapped_type;
  - using folly::F14FastMap<StreamId, StreamDetails>::size;
  - using folly::F14FastMap<StreamId, StreamDetails>::value_type;
  + using folly::F14ValueMap<StreamId, StreamDetails>::cbegin;
  + using folly::F14ValueMap<StreamId, StreamDetails>::cend;
  + using folly::F14ValueMap<StreamId, StreamDetails>::const_iterator;
  + using folly::F14ValueMap<StreamId, StreamDetails>::empty;
  + using folly::F14ValueMap<StreamId, StreamDetails>::find;
  + using folly::F14ValueMap<StreamId, StreamDetails>::mapped_type;
  + using folly::F14ValueMap<StreamId, StreamDetails>::size;
  + using folly::F14ValueMap<StreamId, StreamDetails>::value_type;
  };
  // Details about each stream with frames in this packet
  