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The main motivation is to fix the bug, where KRunner is always displayed on the left monitor (427069). Being able to move a window to a different output on wayland is only the first of two steps required to resolve the problem. The second one is the ability to query the active output on wayland.

In total 3 components have to be patched in order to make it possible to set the output for a window.

1. This MR updates KWayland and with this change, clients are able to send the request.
2. This MR updates KWayland-Server to emit a signal, if a client sends a request.
3. This MR updates KWin to listen for this signal and move the client. (Discussion is here)

I created a small application for testing purposes. Just use git clone https://invent.kde.org/juliuszint/helloqt and checkout the move-to-output branch. If your compiled KWayland library is not at its default location $HOME/kde/build/kwayland, then you will have to adjust the CMakeLists.txt file.

Otherwise it should just compile (TM) and when the button is clicked, the window will be moved onto every output once (delayed by 2 seconds).