server: request xdg-shell v2

Wlroots does not yet support the newer xdg-shell versions and now
requires the compositor to set the supported xdg-shell version during
creation. Set this to v2 for sway as well.

Fixes swaywm#7001

sway/server.c

@@ -126,7 +126,7 @@ bool server_init(struct sway_server *server) {
 		&server->layer_shell_surface);
 	server->layer_shell_surface.notify = handle_layer_shell_surface;
 
-	server->xdg_shell = wlr_xdg_shell_create(server->wl_display);
+	server->xdg_shell = wlr_xdg_shell_create(server->wl_display, 2);
 	wl_signal_add(&server->xdg_shell->events.new_surface,
 		&server->xdg_shell_surface);
 	server->xdg_shell_surface.notify = handle_xdg_shell_surface;