title: mat-select required cannot be reset
body: <p>Each formGroup using a mat-select as the only required field cannot be reset with FormGroup.reset() because validators are not reset</p>
  
  <p><a href="https://stackblitz.com/edit/material7-template-matselect-required?file=src%2Fapp%2Fapp.component.html" rel="nofollow noreferrer">https://stackblitz.com/edit/material7-template-matselect-required?file=src%2Fapp%2Fapp.component.html</a></p>
  
  <p>when submitting, the first field is empty &amp; mark as error...</p>
  
  <p>Only solution that worked for me is to use ngIf to regenerate form but its not really nice for the user that see an empty html for a sec...</p>
  
  <p>Any other solution ?</p>
  
  <p>Thanks !</p>