title: Check if coupon is applied in woo commerce
body: <p>I need to find a way to check if a coupon is applied to Woocommerce checkout, if so I would like to do something.  I have tried searching around for this and cannot find a solution.</p>
  
  <p>here is a slimmed down version of what I am trying:</p>
  
  <pre><code>add_action('woocommerce_before_cart_table', 'apply_product_on_coupon');
  function apply_product_on_coupon( ) {
      global $woocommerce;
      $coupon_id = '12345';
  
          if( $woocommerce-&gt;cart-&gt;applied_coupons === $coupon_id ) {
          echo 'YAY it works';
      }
  }
  </code></pre>
  
  <p>So is this not the right way to check if the coupon exists in cart? <code>if( $woocommerce-&gt;cart-&gt;applied_coupons === $coupon_id )</code></p>