Function TrackField

3rdparty/flatbuffers/include/flatbuffers/flatbuffers.h:678–681

When writing fields, we track where they are, so we can create correct vtables later.

  // When writing fields, we track where they are, so we can create correct
  // vtables later.
  void TrackField(voffset_t field, uoffset_t off) {
    FieldLoc fl = { off, field };
    offsetbuf_.push_back(fl);
  }

  // Like PushElement, but additionally tracks the field this represents.
  template<typename T> void AddElement(voffset_t field, T e, T def) {