int typeToIdSize() {
    return typeToId.size();
  }
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