[effects] Improve interaction between Glide and SlidingPopups effect

Summary:
The glide effect tried to not animate any window the SlidingPopups
effect animates. But it detected that in a very crude way. It announced
the KDE_SLIDE atom and checked for windows having that property set.

This has a few disadvantages:
* KWindowEffects::isEffectAvailable gets confused as an effect announces
  support for SlidingPopups which doesn't provide SlidingPopups
* The approach can only work for X11 windows
* The approach causes X11 usage in the ctor

With this change the GlideEffect implements a slot for
EffectsHandler::windowDataChanged to detect that the SlidingPopupsEffect
grabbed the window. The X11 atom interaction is removed.

Reviewers: #kwin, #plasma_on_wayland

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D3296