Schema errors due to implicit dependency from language module

Problem/Motivation

This dependency in SiteSettingEntity:

    $fields['langcode'] = BaseFieldDefinition::create('language')
      ->setLabel(t('Language code'))
      ->setDescription(t('The language code for the Site Setting entity.'))
      ->setDisplayOptions('form', [
        'type' => 'language_select',
        'weight' => 10,
      ])
      ->setDisplayConfigurable('form', TRUE);

It leads to error if module 'language' is not installed. Like

Schema errors for core.entity_form_display.site_setting_entity.testsitesettingscreatenew.default with the following errors: core.entity_form_display.site_setting_entity.testsitesettingscreatenew.default:content.langcode.settings.include_locked missing schema

Proposed resolution

Looks like we can just remove setDisplayConfigurable('form', TRUE) here. Because language module itself makes these settings for its fields via hook.

function language_entity_base_field_info_alter(&$fields) {
  foreach ($fields as $definition) {
    // Set configurable form display for language fields with display options.
    if ($definition->getType() == 'language') {
      foreach (['form', 'view'] as $type) {
        if ($definition->getDisplayOptions($type)) {
          // The related configurations will be purged manually on Language
          // module uninstallation. @see language_modules_uninstalled().
          $definition->setDisplayConfigurable($type, TRUE);
        }
      }
    }
  }
}

Remaining tasks

User interface changes

API changes

Data model changes