[php-src] Issue #7944: api to set memory_limit to "at least" this much

Issue: https://github.com/php/php-src/issues/7944 Comment Author: cmb69 > wonder how "unlimited" would be represented in such a function tho, […] There is no "unlimited"; that would just be a very large value, never reached in practise. The memory_limit is internally stored as zend_long and size_t. > This will help OP, but I wonder if there is a chance to add callback for when ini settings are > changed, […] That may be a good idea, or maybe not. Anyhow, what to implement exactly obviously requires discussion, and [warrants an RFC](https://wiki.php.net/rfc/howto). > Also ini_set supposed to return false on failure, but if you try setting ridiculous value like > ini_set('memory_limit', '2K') you'll get old value, […] That is supposed to be fixed as of PHP 8.1.0: https://3v4l.org/psYLo