MatStepper treats steps as `interacted` if you immediately return to a previous step

#### Bug, feature request, or proposal:

Bug

#### What is the expected behavior?

Angular-material forms should be presented in a non-error state when the conditions of the default ErrorStateMatcher are not met (not touched or not submitted)

#### What is the current behavior?

When a form is presented inside a mat-stepper, when traversing to a previous step, the form will be in an error state even if the form is pristine and un-submitted. Any attempt to try to reset the form or FormGroupDirective fails.

#### What are the steps to reproduce?

https://stackblitz.com/edit/angular-material2-issue-fay224

#### What is the use-case or motivation for changing an existing behavior?

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?

#### Is there anything else we should know?

Inizia con la riproduzione StackBlitz collegata e traccia l’interazione di MatStepper con il modulo e con ErrorStateMatcher predefinito quando si torna a uno step precedente. Il lavoro è completato quando un modulo non modificato e non inviato rimane privo di errori tornando a visitare uno step e quando il ripristino del modulo o di FormGroupDirective funziona come previsto.

Scritto dal modello di indicizzazione a partire dal testo della issue.