ensure we can handle non-utf8 string arg values in the deprecator

[i-just]

Description

Steps to reproduce:

• clean 4.16.19 or 5.8.21 install
• create a custom module or plugin with a console controller and a service
• in the console controller, add a method like so:

  public function actionTest(): int
  {
      $t1 = "test \200 me";
      Plugin::getInstance()->myService->test($t1);
      return ExitCode::OK;
  }
  

• in the service, add the following method:

  public function test(string $param1) {
      Craft::$app->getDeprecator()->log(__METHOD__, 'some message');
  }
  

• hit that console controller method, e.g. ddev craft test-plugin/default/test
• observe the error

It can also be achieved if $t1 is set to e.g. random_string(5).

Technically, this can also be reproduced by calling Json::encode() on a string that contains non-UTF8 chars.

Fix:
Running the stack trace string-type argument values via mb_convert_encoding() ensures the stack trace can be properly saved in the database.

Related issues

#18218