Implement AlertCommand in htmx

This command generates a native alert box with the resulting text. Mostly in core this is used in tests. But here's a stab at the documentation.

## AJAX API

Used in tests such as web/core/modules/system/tests/modules/ajax_forms_test/src/Callbacks.php

use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\AlertCommand;

  /**
   * Ajax form callback: Selects 'alert'.
   */
  public static function advancedCommandsAlertCallback($form, FormStateInterface $form_state): AjaxResponse {
    $response = new AjaxResponse();
    $response->addCommand(new AlertCommand('Alert'));
    return $response;
  }

## HTMX

There is no native alert command in htmx, but you can use the on::afterrequest to trigger a command

use Drupal\Core\Htmx\Htmx;

(new Htmx())
  ->get($dialogUrl)
  ->on('::after-request', 'alert("Alert")');

### HTMX commands

• hx-on

I updated my sample after reading more into the on().