feat(ngRepeat): expose the iterating properties over the alias

Expose the properties `$index`, `$first`, `$middle`, `$last`, `$odd` and `$even` as part of the alias

Closes #9582
I think that the idea of `ng-alias="$index as myIndex"` is good and in fact doing it right is not trivial (you have to keep both expressions in sync and try to do so with only one $watch). Let me work on an implementation and discuss that later