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

js/ui/main.js

@@ -125,8 +125,8 @@ function _sessionUpdated() {
 
 function start() {
     // These are here so we don't break compatibility.
-    global.logError = window.log;
-    global.log = window.log;
+    global.logError = globalThis.log;
+    global.log = globalThis.log;
 
     // Chain up async errors reported from C
     global.connect('notify-error', (global, msg, detail) => {