public static ExpressionNode transformFunctionNode(FunctionNode node, TypeContext<Reference> context) {
        switch (node.getFunction()) {
            case min:
            case max:
                return transformMaxAndMinFunctionNode(node, context);
        }
        return node;
    }
Transforms min(tensor,dim) and max(tensor,dim) to
reduce(tensor,min/max,dim). This is necessary as the backend does
not recognize these forms of min and max.

@author lesters
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/transform/TensorMaxMinTransformer.java