Incorrect parameter documentation for FormBuilder::submitForm

Problem/Motivation

API page: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Form%21Fo...

The first parameter $form_arg for the FormBuilder::submitForm function is documented as:

\Drupal\Core\Form\FormInterface|string $form_arg: A form object to use to build the form, or the unique string identifying the desired form. If $form_arg is a string and a function with that name exists, it is called to build the form array.

Upon looking at the source code of the function, I've found out that the parameter cannot be a "unique string identifying the desired form". Because if it is a string, then the FormBuilder::getFormId function throws this exception:

 if (!is_object($form_arg) || !($form_arg instanceof FormInterface)) {
    throw new \InvalidArgumentException("The form argument $form_arg is not a valid form.");
  }

Proposed resolution

The documentation for the parameter should be changed to:

\Drupal\Core\Form\FormInterface|string $form_arg: The value must be one of the following:

1. The name of a class that implements \Drupal\Core\Form\FormInterface.
2. An instance of a class that implements \Drupal\Core\Form\FormInterface.

Remaining tasks

• Update documentation.