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/2322closes#2322
