Increase field label maxlength

Problem/Motivation

Sometimes we need to set larger labels on field instances. One example might be on boolean fields where we can use the label as string to display text at the checkbox.
Right now, by default the textfield form element \Drupal\Core\Render\Element\Textfield sets the maxlength to 128

/**
   * {@inheritdoc}
   */
  public function getInfo() {
    $class = get_class($this);
    return [
      '#input' => TRUE,
      '#size' => 60,
      '#maxlength' => 128,
    ...
    ...

and the label (\Drupal\field_ui\Form\FieldConfigEditForm::form) element doesn't provide any alternative \Drupal\field_ui\Form\FieldConfigEditForm::form

    // Build the configurable field values.
    $form['label'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Label'),
      '#default_value' => $this->entity->getLabel() ?: $field_storage->getName(),
      '#required' => TRUE,      
      '#weight' => -20,
    ];

So the maxlength is set to the defaults (128)

Proposed resolution

The proposed solution is to set the #maxlength to a higher value, for instance 255. Since it is a config entity, we should not have conflicts with the database model.

Release notes snippet

Field labels can now be up to 255 characters long. This has no impact on the API, but require attention in admin themes to account for the longer possible label length.