Move per activity last used desktop tracking to kwin
This functionality was handled by kactivitymanagerd but needs to be inside kwin for the case of switching activity to show an active window. VirtualDesktopManager will remember the last used desktop in every activity and switch to it on activity switches.
I have also added an interface to VirtualDesktopManager that gives a reason for the desktop switch. In slide effect, I used this to prevent slide from happening as a response to activity switches. Animating between desktops on activity switch is disorienting and won't make sense later when each activity has its own unique set of desktops, so we may as well remove it now. @teams/vdg
Edited by Eric Edlund