Possibility to make model $dirty even if nothing was changed #7666

The need for this feature appeared right after PR #7495 was merged. While changes in this PR are absolutely reasonable, there are cases when we want to override this default behaviour.

Real life use case: user is filling a form skipping some required fields. I want to highlight these skipped fields on blur. So, it could be something like this

<input ng-model="data.value"
       ng-model-options="{ 
          updateOn: 'default blur',
          checkForChanges: false (or updateAlways: true) 
       }">