title: WooCommerce query all products with a purchase note
body: <p>I am struggling to get all products that have a purchase note, both simple products and variable products.</p>
  <p><code>WC_Product_Query</code> doesn't seem to be able to do that, as that does not provide a method for purchase notes.
  As it's not meta_data but an actual product field I'm don't see how to do this.</p>
  <p>Has anyone a direction in which I would be able to query the above?</p>