perf(ngModelOptions): do not trigger digest during debounce

[shahata]

BREAKING CHANGE:
This change means that anyone watching $viewValue will no longer see the update immediately for debounced updates

Closes #8814

[matsko]

Could you add a digest surrounding the async validator code inside of runValidators? Async validations will need to run a digest to kick off something like $http.

[shahata]

@matsko I'm not sure why this is needed... $$runValidators will still be followed by a digest even with this change (unless someone calls $commitViewValue or $validate without scope.$apply, but all code inside angular is protected nicely as far as I can see)

[shahata]

Am I missing something?

[matsko]

Ah yes sorry. That's because of $writeModelToScope. You can ignore what I said.

[caitp]

I'm not sure if we need a test case for this, because running or not running a digest seems like an implementation detail that doesn't matter a whole lot --- it's primarily a perf fix, so if it doesn't break any existing tests we should be good.

Maybe someone else will disagree, we'll see

[caitp]

I like the look of the patch though. fwiw