Date/Time: Introduce wp_timezone_string() and wp_timezone() for unified timezone retrieval.
wp_timezone_string() retrieves the timezone from current settings as a string. Uses the timezone_string option to get a proper timezone if available, otherwise falls back to an offset.
wp_timezone() retrieves the timezone from current settings as a DateTimeZone object. Timezone can be based on a PHP timezone string or a ±HH:MM offset.