fix(form): set $submitted to true on child forms when parent is submitted

Closes #10071

BREAKING CHANGE:

Forms will now set $submitted on child forms when they are submitted.
For example:
```
<form name="parentform" ng-submit="$ctrl.submit()">
  <ng-form name="childform">
    <input type="text" name="input" ng-model="my.model" />
  </ng-form>
  <input type="submit" />
</form>

Submitting this form will set $submitted on "parentform" and "childform".
Previously, it was only set on "parentform".

This change was introduced because mixing form and ngForm does not create
logically separate forms, but rather something like input groups.
Therefore, child forms should inherit the submission state from their parent form.