@Override
    public ExpressionNode transform(ExpressionNode node, CONTEXT context) {
        if (node instanceof CompositeNode) {
            node = transformChildren((CompositeNode) node, context);
        }
        if (node instanceof FunctionNode) {
            node = transformFunctionNode((FunctionNode) node, context.types());
        }
        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