Add number index signature to Window

It is `[n: number]: Window`.

Author: sandersn

baselines/dom.generated.d.ts

@@ -17050,6 +17050,7 @@ interface Window extends EventTarget, WindowTimers, WindowSessionStorage, Window
     addEventListener(type: string, listener: EventListenerOrEventListenerObject, options?: boolean | AddEventListenerOptions): void;
     removeEventListener<K extends keyof WindowEventMap>(type: K, listener: (this: Window, ev: WindowEventMap[K]) => any, options?: boolean | EventListenerOptions): void;
     removeEventListener(type: string, listener: EventListenerOrEventListenerObject, options?: boolean | EventListenerOptions): void;
+    [index: number]: Window;
 }
 
 declare var Window: {

inputfiles/addedTypes.json

@@ -517,6 +517,9 @@
                 },
                 "implements": [
                     "WindowEventHandlers"
+                ],
+                "override-index-signatures": [
+                    "[index: number]: Window"
                 ]
             },
             "URLSearchParams": {