void save(Object key, Object value) {
    if (value instanceof PdxType) {
      PdxType type = (PdxType) value;
      typeToId.put(type, (Integer) key);
    } else if (value instanceof EnumInfo) {
      EnumInfo info = (EnumInfo) value;
      enumToId.put(info, (EnumId) key);
    }
  }
This map serves two purposes. It lets us look up an id based on a type, if we previously
found that type in the region. And, if a type is present in this map, that means we read
the type while holding the dlock, which means the type was distributed to all members.
geode-core/src/main/java/org/apache/geode/pdx/internal/PeerTypeRegistrationReverseMap.java