Output manager inside KWin

When an output is connected or disconnected, kwin needs to apply a new output configuration to ensure that outputs snap to each other so the pointer can move between outputs, etc. However, kscreen tries to do that too. Furthermore, the drm backend does a step further and reads kscreen's internal data storage to guess the output config.

As a way to clean up output configuration logic, I think that kwin_wayland has to have kscreen or any other output manager running inside it so the output config can be queried directly.