code: public RecordType getOrCreateRecordType(Map<String, SoyType> fields) {
      return recordTypes.intern(RecordType.of(fields));
    }
docs: Factory function which creates a record type, given a map of fields. This folds map types with
  identical key/value types together, so asking for the same key/value type twice will return a
  pointer to the same type object.
  
  @param fields The map containing field names and types.
  @return The record type.