Move active output tracking to workspace
Active output is a window management concept. It indicates what output new windows have to be placed on if they have no output hint. So Workspace seems to be a better place for it than the Screens class, which is obsolete.
Effectively, this resurrects Workspace::activeScreen(). https://invent.kde.org/unmaintained/kde-workspace/-/blob/KDE/4.3/kwin/workspace.h#L286
Edited by Vlad Zahorodnii