Create named closures like Closure::fromCallable()

[nicolas-grekas]

Also found by the differential fuzzing of the polyfill against the extension.

deepclone_from_array() gave the closure over a method the scope of the class it looked the method up on. For an inherited method, the private properties of the parent class weren't reachable anymore:

class Base { private $secret = 'base'; function reveal() { return $this->secret; } }
class Child extends Base {}
$f = deepclone_from_array(deepclone_to_array((new Child)->reveal(...), null, true), null, true);
$f(); // Warning: Undefined property: Child::$secret

The closure now gets the scope of the class that declares the method, and is called on the class of its object or on the named class, like with Closure::fromCallable(). For static methods, deepclone_to_array() exports that called class instead of the declaring one, as the polyfill does, so that static:: resolves the same.

Named closures over a non-static method without an object, or over a method of a class that their object or class doesn't extend, are now rejected, a top-level one whose function doesn't exist throws instead of returning null, the ones over a method that __call() or __callStatic() handles are created with Closure::fromCallable(), and on PHP 8.4+ the shape of the ones lazy objects hold is checked right away, as the README says for malformed payloads.