[php-src] Issue #8532: Allow nullable haystack in string-functions

Issue: https://github.com/php/php-src/issues/8532 Author: Wuschba ### Description Hello, since PHP 8.1. this throws an E_DEPRECATED: ``` $haystack= null; if (str_contains($haystack, "needle")) { ... } ``` I understand that the correct usage of types is important for a clean programming, but whats the reason that $haystack could not be nullable in string-functions? For example: We fetch a lot values from the database in our workflows, and the text-values there can be null as well of course, so in PHP 7.x it was a straight approach just to use: ``` $haystack = getTxtDatabaseValue("txtfield"); // returns ?string if (strpos($haystack, "needle") === false) { ... } ``` just meaning: If $haystack is null, "needle" can not be inside $haystack, so strpos(null, "needle") always returns false. Of course we can do something like: ``` $haystack = getDatabaseValue(); // returns ?string if ($haystack !== null && str_contains($haystack, "needle")) { ... } ``` but the extra check is somehow inconvenient, and of course this breaks a lot of our existing code, which makes the update of the PHP version very expensive. So it would be great if you could consider to allow a nullable string here or perhaps explain to me why it doesn't make sense to allow nullables in string-functions.