Interpolate name attribute in NgModelController

[andrewdavey]

When generating repeated form inputs, setting the name attribute to be an expression does not populate the form.XXX.$invalid, etc, properties.

For example:

<form name="form">
  <div ng-repeat="item in items" ng-class="{ 'error': form[item.key].$invalid }">
    <input type="text" name="{{item.key}}" ng-model="item.value" />
  </div>
</form>

I believe this is due to the following line in NgModelController:
https://github.com/angular/angular.js/blob/master/src/ng/directive/input.js#L937

Could this be enhanced by using $interpolate to evaluate the intended name?

[pkozlowski-opensource]

This is duplicate of #1404
There are several PRs for this already, we just need to review them.