Problem: I would like to output an index value when looping over a repeating field instanced with wpv-for-each.

Solution: You'll need a custom shortcode to do this. Add the following custom shortcode definition in your child theme's functions.php file, or in a new snippet in Toolset > Settings > Custom Code.

add_shortcode('wpv-index', function () {
 
    static $i = 0;
    $n = $i++;
     
    return $n;
});

That will create a shortcode wpv-index, which we can use in the wpv-for-each loop to create these carousel-indicators list items.

Next, use wpv-for-each to iterate over the fotografia field instances and generate the indicator list items:

[wpv-for-each field='wpcf-fotografia']
<li data-target="#carousel" data-slide-to="[wpv-index]"></li>
[/wpv-for-each]