xdg-shell: use toplevel geometry to adjust the popup box

`popup_unconstrain` uses view coordinates to init the output box for
popups. However wlroots expects the box to be set in a toplevel surface
coordinate system, which is not always equal to view. The difference
between those is a window geometry set via xdg-shell.

GTK4 reserves some space for client-side decoration and thus has a
window with top left corner not matching to (0, 0) of a surface. The box
calculated without taking that into account was slightly shifted
compared to the actual output and allowed to position part of the popup
off screen.

sway/desktop/xdg_shell.c

@@ -72,8 +72,8 @@ static void popup_unconstrain(struct sway_xdg_popup *popup) {
 	// the output box expressed in the coordinate system of the toplevel parent
 	// of the popup
 	struct wlr_box output_toplevel_sx_box = {
-		.x = output->lx - view->container->pending.content_x,
-		.y = output->ly - view->container->pending.content_y,
+		.x = output->lx - view->container->pending.content_x + view->geometry.x,
+		.y = output->ly - view->container->pending.content_y + view->geometry.y,
 		.width = output->width,
 		.height = output->height,
 	};