Add loop index in paragraph.html.twig

The paragraph.html.twig template file doesn't have the current loop index available to it, so we have no idea what item is currently being rendered - it is useful sometimes to know what the index is, as we might want to set some different css classes or similar on specific indexes.

To work around this, I added a field hook in my template:

function mytheme_preprocess_field(&$variables) {
    if($variables['field_name'] == 'my_paragraph_field'){

     foreach($variables['items'] as $idx => $item) {
        $variables['items'][$idx]['content']['#paragraph']->index = $idx;
      }
    }
}

This enables me to access the index in the twig template using paragraph.index, but it would be preferable if this or something similar was available natively.