[touch-events] Index TouchList as array

myTouchList[123] is allowed as an alias for myTouchList.item(123).

https://developer.mozilla.org/en-US/docs/Web/API/TouchList
and
http://www.w3.org/TR/touch-events/#idl-def-TouchList

touch-events/touch-event-tests.ts

@@ -16,6 +16,7 @@ flag = touchEvent.shiftKey;
 
 var len:number = list.length;
 touch = list.item(0);
+touch == list[0];
 
 var x: number;
 var y: number;

touch-events/touch-events.d.ts

@@ -16,6 +16,7 @@ interface TouchEvent extends UIEvent {
 interface TouchList {
     length: number;
     item: (index: number) => Touch;
+    [index: number]: Touch;
 }
 
 interface Touch {