[php-src] Issue #11190: Undeprecate strftime() because the rationale for deprecating it doesn't make sense

Issue: https://github.com/php/php-src/issues/11190 Author: mikkorantalainen ### Description The function strftime() is deprecated because it's not thread safe because setlocale() is not thread safe. However, the function sprintf() is similarly dependant on current locale and it's not deprecated! I think it would be much better idea to move locale settings to thread specific data area and keep allowing use of strftime() and sprintf() without weird edge cases in case of threaded (as opposed to process based) web server. This solution is already used for thread-safe gettext variants so it should work in practice. I repeat, the problem is not that strftime() or sprintf() wouldn't be thread safe; the problem is that setlocale() is not thread safe. It would make more sense to deprecate setlocale() if you don't want to change its semantics to change only the locale of the current thread. And then introduce another function with thread specific semantics to set locale. Note that you already have created non-standard behavior because Windows variant of PHP already has thread-specific locale as of PHP 7.0.5: https://www.php.net/setlocale – it would make more sense to standardize this behavior for all platforms because it would make PHP behave the same on all platforms *and* fix the non-thread-safe behavior of sprintf() and strftime() without deprecating anything.