Fix the issues reported by phpcs

Thanks @himanshu_jhaloya, MR looks good all errors and warnings are fixed now.
So moving it to RTBC

+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Drupal\Core\Config\ConfigFactoryInterface;

use statements are alphabetically ordered.

+  /**
+   * The Config Form.
+   *
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   The config factory.
+   */
+  public function __construct(ConfigFactoryInterface $config_factory) {
+    $this->configFactory = $config_factory;

The short description for a constructor starts with Constructs a new and ends with the class name (namespace included) and object.

   public function buildForm(array $form, FormStateInterface $form_state) {
-    $config = \Drupal::service('config.factory')->getEditable('mail_login.settings');
+    $config = $this->configFactory->getEditable('mail_login.settings');

A class that extends ConfigFormBase uses $this->config().

The merge requests branches have conflicts with t=8.x-2.x branch. I had to rewrite the patches.

mqanneh → closed merge request !5

mqanneh → closed merge request !7