Docs enhancements (#18985)

- added more strict checks in if condition: that if `$user` exists, only then call its method
 - Renamed `verifyPassword` to `validatePassword` because yii2-advanced-template use that method name

framework/filters/auth/HttpBasicAuth.php

@@ -37,7 +37,7 @@ namespace yii\filters\auth;
  *             'class' => \yii\filters\auth\HttpBasicAuth::class,
  *             'auth' => function ($username, $password) {
  *                 $user = User::find()->where(['username' => $username])->one();
- *                 if ($user->verifyPassword($password)) {
+ *                 if ($user && $user->validatePassword($password)) {
  *                     return $user;
  *                 }
  *                 return null;