* Add `zend_get_attribute_object()`
This makes the implementation for `ReflectionAttribute::newInstance()`
reusable.
* Add test for the stack trace behavior of ReflectionAttribute::newInstance()
This test ensures that the `filename` parameter for the fake stack frame is
functional. Without it, the stack trace would show `[internal function]` for
frame `#0`.
* Fix return type of `call_attribute_constructor`
Tim Düsterhus