[RFC] Deprecate dynamic properties

Hi internals, I'd like to propose the deprecation of "dynamic properties", that is properties that have not been declared in the class (stdClass and __get/__set excluded, of course): https://wiki.php.net/rfc/deprecate_dynamic_properties This has been discussed in various forms in the past, e.g. in https://wiki.php.net/rfc/locked-classes as a class modifier and https://wiki.php.net/rfc/namespace_scoped_declares / https://github.com/nikic/php-rfcs/blob/language-evolution/rfcs/0000-language-evolution.md as a declare directive. This RFC takes the more direct route of deprecating this functionality entirely. I expect that this will have relatively little impact on modern code (e.g. in Symfony I could fix the vast majority of deprecation warnings with a three-line diff), but may have a big impact on legacy code that doesn't declare properties at all. Regards, Nikita