Make sure that effect windows outlive effects
Compositing is suspended/finished in a very hard way fashion, effect
windows are destroyed without notifying effects about it.
AnimationEffect tries gracefully release deleted windows, but because
in some cases(like when suspending compositing) a deleted window can
be already destroyed, a segmentation fault can happen.
This change adjusts the order in which effect windows and effects are
destroyed, so AnimationEffect (and other effects) cannot access dangling
Reviewers: KWin, graesslin
Reviewed By: KWin, graesslin
Subscribers: graesslin, kwin
Differential Revision: https://phabricator.kde.org/D17311