[php-src] Issue #9965: Non-pure default arguments are mistakenly cached

Issue: https://github.com/php/php-src/issues/9965 Author: iluuu1994 ### Description PHP compiles function default arguments to constant ASTs. The AST is evaluated when the function is called. When the result of the evaluation is a non-refcounted value, PHP assumes that the AST is pure (will always evaluate to the same value) and will then cache the value and skip re-evaluation in the next function call. This assumption is incorrect. ```php <?php class Foo { public function __toString() { static $i = 0; return (string) $i++; } } function test(string $foo = new Foo() . '') { var_dump($foo); } test(); test(); test(); ``` Resulted in this output: ``` string(1) "0" string(1) "0" string(1) "0" ``` But I expected this output instead: ``` string(1) "0" string(1) "1" string(1) "2" ``` Instead what should be done is evaluation of the AST should report whether the AST was pure or not. This currently mainly depends on whether new was used. ### PHP Version PHP 8.1 ### Operating System _No response_