public Inspector field(String name) {
            int offset = hashlet.getIndexOfKey(name);
            if (offset < 0) {
                return invalid();
            }
            return valueAt(offset);
        }
MatchFeatureData helps pack match features for hits into
inspectable HitValue objects, all sharing the same Hashlet
for the field names.

@author arnej
vespajlib/src/main/java/com/yahoo/data/access/helpers/MatchFeatureData.java