ldap_user added implicit dependency on ldap_authentication

Problem/Motivation

As of commit 44d92d7e, included in LDAP 8.x-4.0.0, the ldap_user submodule has an implicit dependency on ldap_authentication, not listed in ldap_user.info.yml, which can cause a fatal error.

In ldap_user/src/Plugin/Validation/Constraint/LdapProtectedUserFieldConstraintValidator.php (added in commit 44d92d7e), this ldap_user function relies on ldap_authentication existing:

public static function create(ContainerInterface $container): LdapProtectedUserFieldConstraintValidator {
  $plugin = parent::create($container);
  $plugin->setLoginValidator($container->get('ldap_authentication.login_validator'));
  return $plugin;
}

That requires the ldap_authentication.login_validator service exists, but in our situation it does not exist (we use ldap_user to sync some info to Drupal, but do not use LDAP for authentication). In this scenario, trying to edit a user results in a fatal error:
Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: You have requested a non-existent service "ldap_authentication.login_validator". in Drupal\Component\DependencyInjection\Container->get()

Steps to reproduce

1. Enable ldap_user, but do not enable ldap_authentication
2. Edit a user, and click save

Proposed resolution

I do not know the intricacies of #2928091: Current password check incorrect in user edit form well enough so this is probably not the perfect fix, but I think ldap_user.module:ldap_user_entity_base_field_info_alter() should at least be modified to fence the new constraint with a \Drupal::service('module_handler')->moduleExists('ldap_authentication') check.

Remaining tasks

Hopefully someone knowledgeable about #2928091: Current password check incorrect in user edit form can weigh in on the fix.