Review the approach of showing confirmation messages

Problem/Motivation

Right now we are checking for `status_messages` block placed in the active theme, and using that block to render the confirmation message when product is added to cart.

AjaxAddToCartForm::refreshAddToCartForm()

    $block = self::getStatusMessagesBlock();
    if ($block) {
      $elements = [
        '#type' => 'status_messages',
      ];

      $response->addCommand(new RemoveCommand('.messages__wrapper'));
      $response->addCommand(new AppendCommand(".region-{$block->getRegion()}", \Drupal::service('renderer')->renderRoot($elements)));
    }

In my opinion I thought it is the best way to implement #2910738: Ajaxify the confirmation message.

Proposed resolution

Get this approach reviewed by someone. Ask Bojan or Matt Glaman for instance, or just ping in #contrib Drupal Slack channel.

Remaining tasks

TBD

User interface changes

N/A

API changes

N/A

Data model changes

N/A