Don't reimplement validation rules for workflow state add/edit forms in ::copyFormValuesToEntity

Problem/Motivation

Right now, in order to save the values a user has entered, we overriding EntityForm::copyFormValuesToEntity in all of these forms:

• WorkflowStateEditForm
• WorkflowStateAddForm
• WorkflowTransitionAddForm
• WorkflowTransitionEditForm

Since the workflows is strict about the validity of the states and transitions it will add to a workflow, if you enter an invalid machine name for example, an exception is triggered which bubbles up to the user.

In #2842193: Exception in Workflow::addState when an invalid machine name is given we fixed this by reimplementing the validation provided by the machine_name element and the validateForm method in order to prevent this from happening:

  class WorkflowStateAddForm {
  ...
  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
    // Replicate the validation that Workflow::addState() does internally as the
    // form values have not been validated at this point.
    if (!$type_plugin->hasState($values['id']) && !preg_match('/[^a-z0-9_]+/', $values['id'])) {
      $type_plugin->addState($values['id'], $values['label']);
    }
  }

It seems this was only done for states however, because the transition forms had already solved this another way:

  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
    if (!$form_state->isValidationComplete()) {
      // Only do something once form validation is complete.
      return;
    }

Proposed resolution

For consistency, lets use the same strategy everywhere and at the same time make things more DRY by not reimplementing validation rules.

Remaining tasks

User interface changes

API changes

Data model changes