xwm: add support for xwayland minimize
Created by: junglerobba
Since https://github.com/swaywm/wlroots/pull/2336 was the wrong approach, I adopted the work from https://github.com/swaywm/wlroots/pull/2264 and I hope I didn't miss any of the open issues on it.
I'm also not quite sure if the minimize event is necessary, so I left it in a separate commit for now.
A patch for sway that simply rejects minimize requests can be found here https://github.com/junglerobba/sway/commit/9a5d8422d3aee1e1c1fa05def9d26cd261cb7398 (caution, because it causes heavy flickering on wine games that were previously acting as described here https://github.com/swaywm/sway/issues/4324 )