Get cart page discounts

Retrieve discounts on the cart page.

 if ( class_exists('\Wdr\App\Controllers\ManageDiscount')) {
                            $manage_discount = new \Wdr\App\Controllers\ManageDiscount();
                            $manage_discount->calculateCartPageDiscounts();
                            $discount_details = \Wdr\App\Controllers\ManageDiscount::$calculated_cart_item_discount;
                            // $discount_details -> details of discounts array
  }