util: Export trySpawn()

It was private before, and so any users of it (including the
Background Apps menu) would fail to utilize it, making apps fail
to get told to shut down from the Background Apps menu.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6893

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2885>

js/misc/util.js

@@ -117,7 +117,7 @@ export function spawnApp(argv) {
  * Runs argv in the background. If launching argv fails,
  * this will throw an error.
  */
-function trySpawn(argv) {
+export function trySpawn(argv) {
     let success_, pid;
     try {
         [success_, pid] = GLib.spawn_async(