ext/pdo: Refactor PDO::FETCH_CLASS to not rely on a FCI and use a HashTable for ctor_arg

[Girgias]

Commits should be reviewed in order.

This removes the last usage of zend_fcall_info_args_ex() and basically supersedes #9725, which would allow merging #9723.

This also aligns the behaviour of the ctor_arguments to be have like CUFA.

Some follow-up ideas:

• Deprecate the automatic wrapping of by-ref arguments for the constructor
• Figure out how to remove the various dummy fields to reduce the size of the struct