static <K, V> BuilderRef<Map<K, V>> forUnorderedMap() {
        return new DefaultBuilderRef<>(HashMap::new,
                HashMap::new,
                Collections::unmodifiableMap,
                Collections::emptyMap);
    }
Creates a builder reference to an unordered map.

@param <K> Type of key of the map.
@param <V> Type of value of the map.
@return Returns the created map.
smithy-utils/src/main/java/software/amazon/smithy/utils/BuilderRef.java