[effects/slidingpopups] Use single QHash to store animations
Summary:
This patch intends to simplify "management" of animations and reduce
QHash abuse.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D14096