private Map<Item, TaggableItem> createReverseConnectivities(Item root) {
        return populateReverseConnectivityMap(root, new IdentityHashMap<>());
    }
Replaces query terms with their stems

@author Mathias Lidal
@author bratseth
@author Steinar Knutsen
container-search/src/main/java/com/yahoo/prelude/querytransform/StemmingSearcher.java