I'm propose move this method to twig_template_get_attributes function.

What we can get:

1. simplify compilation when php extension avalible (no more conditions like https://github.com/fabpot/Twig/blob/master/lib/Twig/Node/Expression/GetAttr.php#L19 )
2. some extensions (filters) get possibility use it Array sorting by object property or array index #535