Add a way to set the fields to retrieve on the query

This new feature needs tests. But it looks really simple, so great work!

Adding new tests is always a good thing! They look great.

Does this work only for Views, or also must work for custom programmatic queries too? For me it isn't working :(

    $query = Index::load('my_index')->query();
    $query->setOption('search_api_retrieved_properties', ['id', 'title', 'geolocation']);
    $result = $query->execute();
    $resultItem = reset($result->getResultItems());
    dump($resultItem->getFields(FALSE));

- this code dumps empty array of fields.

I've tried it on a custom programmatic query too and no luck.
Did anyone find a solution for this?

According to this, the option name should be: 'search_api_retrieved_field_values'

In my case, it worked with:
$query->setOption('search_api_retrieved_field_values', ['id', 'field_XXX', 'field_YYY']);