wayland: displays: Don't wl_display_roundtrip() on new output

This can lead to a lot of code being executed before the EDID is calculated for the new output, in particular the xfsettingsd code (in zwlr_output_manager_v1_listener.done()) which needs it to match the display profiles.

So it's better to let the compositor do things at its own pace, and call the client's XfceWlrOutputListener from a default .done() listener where you update the data for new outputs that require it (EDID, new status, etc.), rather than connecting it directly.

The above problem arises in particular with labwc 0.9.0 which, perhaps because of wlroots 0.19, disconnects then reconnects virtually all outputs when tty changes, causing xfsettingsd to break the display setup as it cannot match the default profile (or any other profile).