title: Use timestamp with mat-datepicker
body: <p>I'm using Angular Material DatePicker</p>
  
  <p>I receive a timestamp from the API and must send back a timestamp to it, however mat-datepicker use date formats such as ISO 8601 string.</p>
  
  <p>My current work around is to manually convert the data back and forth, when receiving data from the API and before sending it back.</p>
  
  <pre><code>// convert date from timestamp to ISO in order to work with datepicker
     myDate = myDate ? new Date(myDate) : null;
  
  // convert date back to timestamp
     myDate = myDate !== null ? Date.parse(myDate) : null;
  </code></pre>
  
  <p>I don't find this solution very elegant or efficient. Is there a way to directly use timestamps with angular material datePicker? Perhaps using a dateAdapter?</p>