Provide option to only add item to wishlist once.

vmarchuk → made their first commit to this issue’s fork.

Hi, all
For complete happiness the only thing missing is an update of the wishlist block via Ajax:
In commerce_wishlist.module make some changes:
1. add this row to "commerce_wishlist_add_to_wishlist_form_ajax" function:

$response->addCommand(new ReplaceCommand('.wishlist-block', getWishlistBlock()));

2. add 2 functions:

 /**
   * Get wishlist block.
   *
   * @return array|NULL
   *   Return render of wishlist block.
   */
   function getWishlistBlock(): ?array {
    $block_id = getWishlistBlockId();
    if ($block_id !== FALSE) {
      $block = Block::load($block_id);
      $render =  \Drupal::entityTypeManager()->getViewBuilder('block')
        ->view($block);
    }
    return $render ?? NULL;
  }

  /**
   * Gets the machine name of a commerce wishlist block visible on the current page.
   *
   * Returns only the first Wishlist found.
   *
   * @return string|false
   *   Return id of the first commerce wishlist block found on current page.
   *   Returns FALSE if no commerce wishlist block is visible.
   */
  function getWishlistBlockId(): string|false {
    // Returns an array of regions each with an array of blocks.
    $regions = \Drupal::service('block.repository')->getVisibleBlocksPerRegion();
    // Iterate all visible blocks and regions.
    foreach ($regions as $region) {
      foreach ($region as $block) {
        $plugin_id = $block->get('plugin');
        // Check if this is a commerce wishlist block.
        if ($plugin_id === 'commerce_wishlist') {
          return $block->id();
        }
      }
    }

    return FALSE;
  }

luksak → made their first commit to this issue’s fork.

Updating the wishlist block via ajax was accidentally removed in this MR. I just added it back.

Besides that the MR work perfectly for me.