4d454dcb6 Refactoring with QString::toNSString (Hennadii Stepanov)
Pull request description:
This PR makes `MacNotificationHandler::showNotification()` cleaner and more readable. The used `QString::toNSString()` function was introduced in Qt 5.2 which is minimum version now (#14725). The behavior of `MacNotificationHandler::showNotification()` has not been changed. cc: @jonasschnelli
Backport of Core PR14975