WLCS relies on implicit focus on creation

[elinorbgr]

It appears some tests (like CopyCutPaste for example) rely on the fact that a newly created window would automatically get keyboard focus on creation.

As far as I can tell, this is not something standardized in the protocol and rather this is compositor policy. So I suppose it would make sense to instead add a function to the wlcs_display_server interface so that WLCS can explicitly require from the compositor that a certain surface be given keyboard focus? This would typically be used in cases like this create_surface_with_focus function:

https://github.com/MirServer/wlcs/blob/8eac3ad2f31676c3d22c7ac5dad4cb8cb8205291/tests/copy_cut_paste.cpp#L85-L88