feat(ngModel): add public $setModelValue fn to programmatically update model

[tdakhla]

In regards to my workaround in #11090 (comment), it would be nice to have a $setModelValue fn in NgModelController which would programmatically update the model. Instead of having to inject in $parse to my directive, do $parse(attrs.ngModel).assign(scope, newValue), etc, (I've seen code like this in several places, and I've used it a lot in my directives), there should be a public fn to do that work.

The code in NgModelController should be as easy as:

this.$setModelValue = function(value) {
    ngModelSet($scope, value);
};

Or, if all the $viewChangeListeners need to get executed, then perhaps open up this.$$writeModelToScope by changing it so it accepts a model value param, and rename it to this.$setModelValue (and doing the handful of refactors). I think having $setModelValue would be a nice addition to the ngModel API.

[Narretz]

Customizing when / how the model is set to scope is definitely planned. Btw, $setModelValue is a bit confusing as there's also the $modelValue property on ngModel, and I would expect that this is set from this function.

[realityking]

I've got an implementation in #10764, I just haven't had time to adress the last comment.

[maraisr]

+1

[Narretz]

Setting the scope model from inside the ngModel controller so that it runs the model > view pipeline again is not good practice. There might be edge cases where it is necessary, but I'd rather have devs use parse and assign in this case, then expose a function on the ngModelController that does it.
For the simple case where you need to re-run the formatters on the modelValue, there will be a function in 1.6.7: 1451948