Deprecate user_validate_name() and replace with service

UserPasswordForm has a copy-paste of user_validate_name() that could also be replaced here:

    // First, see if the input is possibly valid as a username.
    $name = trim($form_state->getValue('name'));
    $definition = BaseFieldDefinition::create('string')
      ->addConstraint('UserName', []);
    $data = $this->typedDataManager->create($definition);
    $data->setValue($name);
    $violations = $data->validate();
    // Usernames have a maximum length shorter than email addresses. Only print
    // this error if the input is not valid as a username or email address.
    if ($violations->count() > 0 && !$this->emailValidator->isValid($name)) {

Have not reviewed

But appears to have several test failures.

Searched for user_validate_name() and appears all instances have been replaced.

Based on the small number in core assume that D11 should be fine for removal vs D12.

Test coverage can be seen here https://git.drupalcode.org/issue/drupal-3431203/-/jobs/1099143

I've added some review comments to address - thanks!

For the @return statement. If phpcs doesn't complain about it being included think it can't hurt.

Feedback appears to be addressed.

Given where we are in the release cycle and the number of usages I think we should push the deprecation of user_validate_name out to 12. See https://git.drupalcode.org/search?group_id=2&repository_ref=&scope=blobs...

Also I think we should update the code to call the new service for consistency.

Pushed the minor tweaks for #14

Committed 8e7d3e0 and pushed to 11.x. Thanks!
Committed 3194f76 and pushed to 10.3.x. Thanks!