[php-src] Issue #9784: DateTime:: and DateTimeZone::__construct should throw a dedicated exception if the input is invalid

Issue: https://github.com/php/php-src/issues/9784 Author: Daimona ### Description If DateTime::__construct or DateTimeZone::__construct receive invalid input, they will throw a generic Exception ([3v4l for DateTime](https://3v4l.org/M3u7H), [3v4l for DateTimeZone](https://3v4l.org/MUPlM)). This contradicts the general principle that you should always use a dedicated exception type, and not the generic Exception class. While it's less of a problem for PHP internal code, things could still go wrong. The main example is that you may be using a PHP extension that can throw exceptions while PHP executes the constructor call. For instance, Wikimedia uses the [Excimer](https://www.mediawiki.org/wiki/Excimer), which allows you to set interrupting timers, and a dedicated exception (TimeoutException) is thrown as soon as the timer expires. In practice, this means that whenever we want to instantiate a potentially invalid DateTime(Zone), the code will look like this: ```php try { $x = new DateTimeZone( $somethingPotentiallyInvalid ); } catch ( TimeoutException $e ) { throw $e; } catch ( Exception $_ ) { // Handle invalid time zone } ``` This is not ideal, because you need to remember about TimeoutException possibly being thrown. A dedicated exception would make it much more readable and straightforward, for instance: ```php try { $x = new DateTimeZone( $somethingPotentiallyInvalid ); } catch ( InvalidTimeZoneException $e ) { // Handle invalid time zone } ``` This change would also be backwards compatible, except for places (not too common, I guess) where someone does things like: ```php try { $x = new DateTimeZone( $somethingPotentiallyInvalid ); } catch ( Exception $e ) { if ( get_class( $e ) === Exception::class ) { // ... } ```