Make it so tip is added when it's selected instead of Erroring

So The error message here was part of #3564307: Cannot add tip. That said, this is still a usability option IMO incase they forget to hit the "Add" button but have an item selected. I think this will make it so that store operators dont' miss out on much wanted tip transactions due to a usability issue and the user not noticing or not wanting to go back and correct it.

As an FYI this will require some duplication of AddTip since that function and the submitInlineForm() function seem to handle how to grab from $form_state a bit differently.

FYI I created a custom module to overload the contrib module's InlineForm because I wanted to do some other work around building the form as well... This is what I ended up with in my submit handler:

  public function submitInlineForm(array &$inline_form, FormStateInterface $form_state) {
    $values = $form_state->getValue($inline_form['#parents']);
    $inline_configuration = $form_state->get('inline_configuration');
    /** @var \Drupal\commerce_order\Entity\Order $order */
    $order = \Drupal::entityTypeManager()->getStorage('commerce_order')->load($inline_configuration['order_id']);
    $total_price = $order->getTotalPrice();
    $tip = $values['tip_info']['tip'];
    if ($values['tip_info']['tip_options'] && $values['tip_info']['tip'] == 'other') {
      $tip = $values['tip_info']['other_tip'];
    }
    elseif ($values['tip_info']['tip_options'] && $values['tip_info']['tip'] !== 'none') {
      $tip = round((float) $total_price->getNumber() * (float) $values['tip_info']['tip'], 2);
    }
    if ($values['tip_info']['tip'] !== 'none' && !empty($tip)) {
      $order->addAdjustment(new Adjustment([
        'type' => 'custom',
        'label' => 'Tip',
        'amount' => new Price($tip, $total_price->getCurrencyCode()),
        'locked' => TRUE,
        'source_id' => 'custom',
        'percentage' => NULL,
        'included' => FALSE,
      ]))->save();
    }
  }

The differing code is in the first lines... addTip has

    $triggering_element = $form_state->getTriggeringElement();
    $parents = array_slice($triggering_element['#parents'], 0, -1);
    $values = $form_state->getValue($parents);

Where mine has

    $values = $form_state->getValue($inline_form['#parents']);

and then goes on to reference the values in the $values variable using the full array key syntax like $values['tip_info']['tip'] instead of $values['tip']

Hope this helps.