Update output propertes on mode change

This was previously done when arranging the output, but only needs to be
done on mode change.

sway/desktop/output.c

@@ -505,6 +505,10 @@ static void handle_destroy(struct wl_listener *listener, void *data) {
 
 static void handle_mode(struct wl_listener *listener, void *data) {
 	struct sway_output *output = wl_container_of(listener, output, mode);
+	output->lx = output->wlr_output->lx;
+	output->ly = output->wlr_output->ly;
+	wlr_output_effective_resolution(output->wlr_output,
+			&output->width, &output->height);
 	arrange_layers(output);
 	arrange_output(output);
 	transaction_commit_dirty();