[RFC] Deprecate and remove case-insensitive constants

Hi internals, I'd like to propose the deprecation (in PHP 7.3) and removal (in PHP 8) of case-insensitive constants: https://wiki.php.net/rfc/case_insensitive_constant_deprecation This was already discussed some time ago on the list, though that discussion degenerated into unfortunate directions. I'd very much appreciate if we could keep discussions on making PHP fully case-sensitive or fully case-insensitive outside of this thread. (Feel free to open a new one though.) The main point I'd like to have feedback on is the handling of true, false and null, as I'm not sure what the best approach regarding that is. Regards, Nikita