title: Common file in variable product
body: <p>I want to have Variable Products that grant access to a specific file no matter the Variation. I tried simply enabling the <code>downloadable</code> button for variable products and overriding <code>is_downloadable</code> however while the data in the REST API is like I want it, in the product editor <code>downloadable</code> is unchecked and <code>Downloadable files</code> is hidden until it is checked again.</p>
  <p>My simple plugin currently looks like this</p>
  <pre><code>function enable_downloadable($product_type_options)
  {
      $product_type_options['downloadable']['wrapper_class'] = 'show_if_simple show_if_variable';
      $product_type_options['downloadable']['default'] = 'yes';
      $product_type_options['virtual']['wrapper_class'] = 'show_if_simple show_if_variable';
      $product_type_options['virtual']['default'] = 'yes';
      return $product_type_options;
  }
  add_filter( 'product_type_options', 'enable_downloadable' );
  
  function is_downloadable($downloadable, $product)
  {
      return 'yes';
  }
  add_filter('woocommerce_is_downloadable', 'is_downloadable', 10, 2);
  
  function is_virtual($virtual, $product)
  {
      return 'yes';
  }
  add_filter('woocommerce_is_virtual', 'is_virtual', 10, 2);
  
  function save_metadata($post_id)
  {
      update_post_meta( $post_id, '_downloadable', 'yes' );
      update_post_meta( $post_id, '_virtual', 'yes' );
  }
  
  add_action( 'woocommerce_process_product_meta_variable', 'save_metadata');
  add_action( 'woocommerce_process_product_meta_simple', 'save_metadata');
  </code></pre>
  <p>Any simple way to achieve this?</p>