dbusServices: Refactor service utilities from fileUtils into dbusUtils

To enable porting services to ECMAScript modules independently of
the shell, split DBus service utility functions into a new file,
dbusUtils.js

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2365>

js/dbusServices/extensions/extensionsService.js

@@ -5,7 +5,7 @@ const { Gio, GLib, Shew } = imports.gi;
 
 const ExtensionUtils = imports.misc.extensionUtils;
 
-const { loadInterfaceXML } = imports.misc.fileUtils;
+const { loadInterfaceXML } = imports.misc.dbusUtils;
 const { ExtensionPrefsDialog } = imports.extensionPrefsDialog;
 const { ServiceImplementation } = imports.dbusService;