Issue #1925272 by super_romeo, hswong3i: Timezone: Add hook_alter to handle User timezones

  // Add user timezone to time.

  // Assume that all owned entities (for example, offices) should

  // depend on user timezone.

  // Use case is a website as bulletin board.

  // Multiple accounts (clients) with different cities and timezones.

  // Client sets his timezone in his account data.

  // His articles (offices) have office hours with current status (open\closed).

  // Client sets it to e.g., 8:00-20:00.

  // Visitor chooses his city and wants to see if offices in this city are open.

  if ($entity instanceof \Drupal\user\EntityOwnerInterface

    && ($account = $entity->getOwner())

    && ($account->isAuthenticated())