xdg_shell: configure surface on initial commit

Instead of waiting for the surface to be mapped before sending a
configure event, do it on initial commit.

Note, wlroots 0.18 no longer sends automatic configure events on
initial commit.

xdg_shell.h

@@ -12,6 +12,7 @@ struct cg_xdg_shell_view {
 	struct wlr_xdg_toplevel *xdg_toplevel;
 
 	struct wl_listener destroy;
+	struct wl_listener commit;
 	struct wl_listener unmap;
 	struct wl_listener map;
 	struct wl_listener request_fullscreen;