feat(input): interpolates form input name attrs for ngModel

@frankhuster / @niargh has brought up an issue with using the `$index` of a repeated element for the name attribute of a form input.

I don't know how common of a use-case it is, but it seems not especially harmful to do a one-time interpolation in post-link.

It shouldn't be a breaking change unless people are using interpolation markers in their names.
there's no way to be sure extra references get cleaned up, we can only clean up references that we know for sure exist.

So what happens is, if the form has a control which matches this control, but form[oldName] is some other control (IE the two controls actually had the same name), then it just makes sure that the control is known before adding the reference.

All known references should be cleaned up on $destroy (further down) --- basically the idea is to just not add a reference if the control isn't known