Support zend_throw_exception_object

[joehoyle]

Currently I believe it's not possible to throw exceptions with state / data attached. For example, if I have an AWSException and I want to add a request property with a given value-- as I can't instantiate AWSException and then throw it (only reference a ClassEntry in PhpException::new()`.

I'm not 100% how the API would look for this, but it would be great to be able to instantiate the exception, and throw that via zend_throw_exception_object instead of zend_throw_exception_ex.