[2.1] Added Zend\Stdlib\StringUtils::hasPcreUnicodeSupport()

The method is a copy of `Zend\Filter\AbstractFilter::hasPcreUnicodeSupport()` but within `Zend\Stdlib\StringUtils` it's more reusable an can be used without `Zend\Filter`.

`Zend\Stdlib` isn't marked as a dependency of `Zend\Filter` but this method is using `Zend\Stdlib\ErrorHandler`. If we mark it as a dependency we could redirect and deprecate the method else the use of `ErrorHandler` should be removed.