cleanup: Mark globals used from other modules as exported

eslint cannot figure out that those symbols are used from other modules
via imports, so they trigger unused-variable errors. To fix, explicitly
mark those symbols as exported.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/627

js/ui/pointerA11yTimeout.js

@@ -1,3 +1,4 @@
+/* exported PointerA11yTimeout */
 const { Clutter, GLib, GObject, Meta, St } = imports.gi;
 const Tweener = imports.ui.tweener;
 const Main = imports.ui.main;