loginManager: Return objects instead of multiple booleans

Multiple booleans - both in arguments and return values - are almost
always problematic API, because people have to memorize (or more likely
look up) the meaning of each position.

Instead, return a JS object so each value has a name attached to it.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2370>

js/misc/systemActions.js

@@ -351,7 +351,7 @@ const SystemActions = GObject.registerClass({
     }
 
     async _updateHaveSuspend() {
-        const [canSuspend, needsAuth] = await this._loginManager.canSuspend();
+        const {canSuspend, needsAuth} = await this._loginManager.canSuspend();
         this._canHaveSuspend = canSuspend;
         this._suspendNeedsAuth = needsAuth;
         this._updateSuspend();