Issue #2858625 by mpdonadio: Daterange formatters should use...

Issue #2858625 by mpdonadio: Daterange formatters should use $date->getTimestamp() instead of $date->format('U')

core/modules/datetime_range/src/DateTimeRangeTrait.php

@@ -23,7 +23,7 @@ public function viewElements(FieldItemListInterface $items, $langcode) {
         /** @var \Drupal\Core\Datetime\DrupalDateTime $end_date */
         $end_date = $item->end_date;
 
-        if ($start_date->format('U') !== $end_date->format('U')) {
+        if ($start_date->getTimestamp() !== $end_date->getTimestamp()) {
           $elements[$delta] = [
             'start_date' => $this->buildDateWithIsoAttribute($start_date),
             'separator' => ['#plain_text' => ' ' . $separator . ' '],

core/modules/datetime_range/src/Plugin/Field/FieldFormatter/DateRangePlainFormatter.php

@@ -48,7 +48,7 @@ public function viewElements(FieldItemListInterface $items, $langcode) {
         /** @var \Drupal\Core\Datetime\DrupalDateTime $end_date */
         $end_date = $item->end_date;
 
-        if ($start_date->format('U') !== $end_date->format('U')) {
+        if ($start_date->getTimestamp() !== $end_date->getTimestamp()) {
           $elements[$delta] = [
             'start_date' => $this->buildDate($start_date),
             'separator' => ['#plain_text' => ' ' . $separator . ' '],