JS: migrate from the global window to globalThis

As of mozjs68 (gjs-1.64) `globalThis` is recommended over `window` and
it makes more sense in this context anyways. Migrate the few instances
of `window` we use and adjust the eslint configuration.

`window` will continue to resolve to `globalThis`, so this won't affect
extensions or other downstream users.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2322

closes #2322

subprojects/extensions-app/js/main.js

@@ -476,7 +476,7 @@ var ExtensionRow = GObject.registerClass({
 function initEnvironment() {
     // Monkey-patch in a "global" object that fakes some Shell utilities
     // that ExtensionUtils depends on.
-    window.global = {
+    globalThis.global = {
         log(...args) {
             print(args.join(', '));
         },