Migrate from KWindowSystem's deprecated methods
This particularly affects src/platforms/linux/windowhelper.cpp
. The deprecated functions we use are:
KWindowSystem::compositingActive()
KWindowSystem::compositingChanged
KWindowSystem::minimizeWindow
This is not a complex issue, just putting here so that I don't forget. In case this change will break something, I want to fix this issue after I can reproducibly build Pisces with Nix.