xwm: add request_close signal

This is especially useful if the compositor wants to support X11
panels to control windows. Without the signal a compositor does
have to hook into the user_event_handler callback but that would
not change the _NET_SUPPORTED root window property.

include/wlr/xwayland/xwayland.h

@@ -171,6 +171,7 @@ struct wlr_xwayland_surface {
 		struct wl_signal request_maximize;
 		struct wl_signal request_fullscreen;
 		struct wl_signal request_activate;
+		struct wl_signal request_close;
 
 		struct wl_signal associate;
 		struct wl_signal dissociate;

include/xwayland/xwm.h

@@ -39,6 +39,7 @@ enum atom_name {
 	WM_TAKE_FOCUS,
 	WINDOW,
 	NET_ACTIVE_WINDOW,
+	NET_CLOSE_WINDOW,
 	NET_WM_MOVERESIZE,
 	NET_SUPPORTING_WM_CHECK,
 	NET_WM_STATE_FOCUSED,