Options/General page: minor tweak to support deprecated timezones

Underneath the time zone selector on the Options/General page, a small snippet of info about the selected time zone is displayed.

This information would be missing if the timezone would be set to a deprecated timezone value, even though PHP is perfectly capable of generating that information, including for deprecated timezones.

By passing the `DateTimeZone::ALL_WITH_BC` constant as the `$timezoneGroup` parameter to the PHP native `timezone_identifiers_list()` function, a timezone name list is retrieved containing both current and deprecated timezone names, preventing the condition from failing when the current timezone is a deprecated one.

See the extensive write-up about this in Trac#56468.

Also see: https://www.php.net/manual/en/datetimezone.listidentifiers.php

As this is an admin/output page, no tests are available or can be set up without jumping through a lot of hoops.

Author: jrfnl

src/wp-admin/options-general.php

@@ -285,7 +285,7 @@
 	?>
 	<br />
 	<?php
-	if ( in_array( $tzstring, timezone_identifiers_list(), true ) ) {
+	if ( in_array( $tzstring, timezone_identifiers_list( DateTimeZone::ALL_WITH_BC ), true ) ) {
 		$transitions = timezone_transitions_get( timezone_open( $tzstring ), time() );
 
 		// 0 index is the state at current time, 1 index is the next transition, if any.