[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
Merge pull request #3379 from hraban/patch-1

[touch-events] Index TouchList as array