Fix getCode when returning anonymous class extending/implementing non FQCN.

[adoy]

Code

use Foo\Bar;

$closure = fn() => new class() extends Bar\Baz {
};
$reflector = new ReflectionClosure($closure);
echo $reflector->getCode();

Current result:

fn() => new class() extends Bar\Baz {
}

Expected result:

fn() => new class() extends \Foo\Bar\Baz {
}