Issue #2071985 by tim.plunkett: Modernize form_test().module forms.

...est/lib/Drupal/form_test/ConfirmFormArrayPathTestForm.php

...es/form_test/lib/Drupal/form_test/ConfirmFormTestForm.php

...orm_test/lib/Drupal/form_test/FormTestArgumentsObject.php

...rm_test/lib/Drupal/form_test/FormTestAutocompleteForm.php

...rm_test/lib/Drupal/form_test/FormTestControllerObject.php

...modules/form_test/lib/Drupal/form_test/FormTestObject.php

.../form_test/lib/Drupal/form_test/FormTestServiceObject.php

...rm_test/lib/Drupal/form_test/SystemConfigFormTestForm.php