Use getAccountName() instead of getDisplayName()

Will review, but I think getAccountName() probably makes more sense. If both cases are needed, we might need to make a configurable option to switch between the two.

Looks like getDisplayName() does call getAccountName().

In this particular method, it's also running any user_format_name alters found. Which I think makes sense.

I would try disabling the name alter and see if it works without it first.

For reference:

public function getDisplayName() {
    $name = $this->getAccountName() ?: \Drupal::config('user.settings')->get('anonymous');
    \Drupal::moduleHandler()->alter('user_format_name', $name, $this);
    return $name;
}

public function getAccountName() {
    return $this->get('name')->value ?: '';
}

Added configuration item that will allow the user to select source for user email/name. By default it will use display name, but you can set it to use account name instead if need be.

See commit above or latest changes in dev branch.