extensions/internals: Port to ESM

We got rid of all uses of extension utils code in the gnome-shell
process itself, and everything that is now using it - including
extensions - is already loaded as module.

We can therefore quickly move the file to ESM, which will help
a bit with upcoming changes.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2837>

js/dbusServices/extensions/extensionsService.js

@@ -5,9 +5,9 @@ import Shew from 'gi://Shew';
 
 import {ExtensionPrefsDialog} from './extensionPrefsDialog.js';
 import {ServiceImplementation} from './dbusService.js';
+import {setExtensionManager} from './extensions/sharedInternals.js';
 
 const {deserializeExtension} = imports.misc.extensionUtils;
-const {setExtensionManager} = imports.extensions.sharedInternals;
 const {loadInterfaceXML} = imports.misc.dbusUtils;
 
 const ExtensionsIface = loadInterfaceXML('org.gnome.Shell.Extensions');