xwm: introduce associate/dissociate events

We'll soon introduce a unified wlr_surface map event. Up until now, compositors
have been using wlr_xwayland_surface's map event to setup various wlr_surface
related listeners (e.g. commit). This will no longer be possible when that
event is moved over to wlr_surface. Introduce new events where the compositor
can add/remove wlr_surface event listeners.

include/wlr/xwayland/xwayland.h

@@ -150,6 +150,9 @@ struct wlr_xwayland_surface {
 		struct wl_signal request_fullscreen;
 		struct wl_signal request_activate;
 
+		struct wl_signal associate;
+		struct wl_signal dissociate;
+
 		struct wl_signal map;
 		struct wl_signal unmap;
 		struct wl_signal set_title;

xwayland/xwm.c

@@ -171,6 +171,8 @@ static struct wlr_xwayland_surface *xwayland_surface_create(
 	wl_signal_init(&surface->events.request_maximize);
 	wl_signal_init(&surface->events.request_fullscreen);
 	wl_signal_init(&surface->events.request_activate);
+	wl_signal_init(&surface->events.associate);
+	wl_signal_init(&surface->events.dissociate);
 	wl_signal_init(&surface->events.map);
 	wl_signal_init(&surface->events.unmap);
 	wl_signal_init(&surface->events.set_class);
@@ -399,6 +401,8 @@ static void xwayland_surface_dissociate(struct wlr_xwayland_surface *xsurface) {
 	xwayland_surface_set_mapped(xsurface, false);
 
 	if (xsurface->surface != NULL) {
+		wl_signal_emit_mutable(&xsurface->events.dissociate, NULL);
+
 		wl_list_remove(&xsurface->surface_commit.link);
 		wl_list_remove(&xsurface->surface_precommit.link);
 		wlr_addon_finish(&xsurface->surface_addon);
@@ -962,6 +966,8 @@ static void xwayland_surface_associate(struct wlr_xwm *xwm,
 	if (xwm->xres) {
 		read_surface_client_id(xwm, xsurface);
 	}
+
+	wl_signal_emit_mutable(&xsurface->events.associate, NULL);
 }
 
 static void xwm_handle_create_notify(struct wlr_xwm *xwm,