ngChange: allow locals to be passed from ngModel

[dcherman]

Do you want to request a feature or report a bug?

Feature

What is the current behavior?

In order to support transient information (metadata) about the operation that occurred for custom controls that implement ngModel, you have to do something like assign the relevant information to a property on your controller and unset it after the $setViewValue call.

What I'm proposing is the ability to pass a $locals argument to $setViewValue that will then be made available in the ngChange expression if one exists.

[gkalpak]

It would have to pass through several layers to get to ngChange 😃
$setViewValue --> debounce --> parse --> validate --> $viewChangeListeners --> ngChange

I'm not sure it's worth the trouble. I wonder if it would be more straight-forward to have a custom directive and augment the NgModelController.

I'm not saying I couldn't get convinved otherwise...

_{(Whatever you do, don't call it $locals though 😛 )}

[dcherman]

@gkalpak It's actually not bad at all. I wrote up a quick PR that accomplishes what I described in #14684. If it seems reasonable, I'll clean it up with tests and docs and get it merge ready.