Enable lookup of the loop's values

[justinbmeyer]

Related to: https://forums.bitovi.com/t/for-of-last-item/1062/3

If you use https://canjs.com/doc/can-stache.addLiveHelper.html, you should be able to make a simple ifLast like:

{{#for(item of itemsArray)}}
      <p {{#ifLast}}class="last"{{/ifLast}}>{{item}}</p>
    {{/for}}

But we'd need a way to lookup the array and list on the scope. Perhaps something like:

stache.registerLiveHelper("ifLast", function(options){
  var index = options.scope.get("scope.index");
  var list = options.scope.get("scope.forOfList")
  return index === list.length - 1 ? options.fn() : options.inverse();
})