More robust TZ handling

src/Plugin/Field/FieldFormatter/IntlTimestampFormatter.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\intl_date\Plugin\Field\FieldFormatter;
 
+use Drupal\Core\Datetime\TimeZoneFormHelper;
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\Plugin\Field\FieldFormatter\TimestampFormatter;
 use Drupal\Core\Form\FormStateInterface;
@@ -75,7 +76,7 @@ class IntlTimestampFormatter extends TimestampFormatter {
     $elements['timezone'] = [
       '#type' => 'select',
       '#title' => $this->t('Time zone'),
-      '#options' => ['' => $this->t('- Default site/user time zone -')] + system_time_zones(FALSE, TRUE),
+      '#options' => ['' => $this->t('- Default site/user time zone -')] + TimeZoneFormHelper::getOptionsListByRegion(),
       '#default_value' => $this->getSetting('timezone'),
     ];