In a views template (views-view-unformatted.twig.html), I have 
 
    {% for row in rows %}  
        {% set row_index = loop.index0 %}  
        {{ row.content }}  
    {% endfor %}  

where each row is processed in a node--view.twig.html.  How can I pass in row_index to the node--view.twig.html?  This is used simply to create an index.