extensions-app: Port to ESM

The extensions app is another part of the code base that is largely
separate from the main code base, and can therefore be ported to
ESM before the big switch.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2786>

subprojects/extensions-app/js/main.js

@@ -1,10 +1,12 @@
-/* exported main */
-imports.gi.versions.Adw = '1';
-imports.gi.versions.Gtk = '4.0';
+import Adw from 'gi://Adw?version=1';
+import GLib from 'gi://GLib';
+import Gio from 'gi://Gio';
+import GObject from 'gi://GObject';
+import Gtk from 'gi://Gtk?version=4.0';
+import Shew from 'gi://Shew';
 
-const Gettext = imports.gettext;
+import * as Gettext from 'gettext';
 const Package = imports.package;
-const { Adw, GLib, Gio, GObject, Gtk, Shew } = imports.gi;
 
 Package.initFormat();
 
@@ -540,9 +542,13 @@ function initEnvironment() {
     };
 }
 
-function main(argv) {
+/**
+ * @param {string[]} argv - command line arguments
+ * @returns {void}
+ */
+export async function main(argv) {
     initEnvironment();
     Package.initGettext();
 
-    new Application().run(argv);
+    await new Application().runAsync(argv);
 }