The existing Data struct has some serious problems:
(a) naming is not intuitive, SlideInterface uses more cleaner terminology
so let's use that (and because Wayland is the future);
(b) fadeInTime and fadeOutTime should be slideInDuration and slideOutDuration
respectively. The Sliding popups effect doesn't fade windows, it slides
them;
(c) mWindowsData should be m_animationsData because other parts of this
effect refer to it as "anim data"(e.g. setupAnimData).
This effect uses its own Location enum class instead of KWayland::
Server::SlideInterface::Location because it would be better to not
depend on platform specific data structures.
As a side effect, this change also fixes QHash abuse. The Sliding popups
effect is still hashing windows twice in prePaintWindow and paintWindow.
But I think that's acceptable because usually there would be only one
active sliding window.