RFC: wayland: Query pkg-config if Xwayland supports listenfd

-listen option is deprecated in favor of the -listenfd option. This change makes kwin query whether Xwayland supports the -listenfd option at build time. If the pkg-config file is missing, we'll use the old listen option.

RFC as I'm not sure that it's a good idea to query the capabilities of runtime dependencies at build time. But it seems like other wayland compositor developers think that it's fine. https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/551#note_793887