WLCS relies on implicit focus on creation

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

Start with tests/copy_cut_paste.cpp, especially create_surface_with_focus, and inspect the wlcs_display_server interface. Determine how WLCS can explicitly request keyboard focus from the compositor instead of relying on creation policy. Done means the affected tests use the explicit focus path and no longer depend on implicit focus.

Written by the indexing model from the issue text.