misc: Fetch environment from launch context before spawn_async()

This will fetch the right environment for the launched application,
without using GNOME Shell's environment.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2993>
(cherry picked from commit 7b1223a254)

js/misc/util.js

@@ -111,8 +111,9 @@ function spawnApp(argv) {
 function trySpawn(argv) {
     var success_, pid;
     try {
+        const launchContext = global.create_app_launch_context(0, -1);
         [success_, pid] = GLib.spawn_async(
-            null, argv, null,
+            null, argv, launchContext.get_environment(),
             GLib.SpawnFlags.SEARCH_PATH | GLib.SpawnFlags.DO_NOT_REAP_CHILD,
             () => {
                 try {