title: Firestore Timestamp.fromDate not UTC
body: <p>Anyone knows how to persist UTC Timestamp in Firestore?</p>
  
  <p>In my <code>Angular</code> app, if I convert today's date to a Timestamp like the following and I end up with a <code>UTC+2</code> (it's summer time here right now in Switzerland) date in the Firestore database</p>
  
  <pre><code>import {firebase} from '@firebase/app';
  import '@firebase/firestore';
  
  const myTimestamp = firebase.firestore.Timestamp.fromDate(new Date());
  </code></pre>
  
  <p>If for example I try to convert a date from the winter time, I end up with <code>UTC+1</code> Timestamp in the database</p>
  
  <pre><code>const myTimestamp = firebase.firestore.Timestamp.fromDate(new Date(2019, 0, 1));
  </code></pre>
  
  <p>If I would use <code>now()</code> I end up with <code>UTC+2</code> dates too</p>
  
  <pre><code>const now: firebase.firestore.Timestamp = firebase.firestore.Timestamp.now();
  </code></pre>
  
  <p>I don't do anything particular when I persist the data:</p>
  
  <pre><code>const now: firebase.firestore.Timestamp = firebase.firestore.Timestamp.now();
  const myTimestamp = firebase.firestore.Timestamp.fromDate(new Date());
  
  const myData = {
      created_at: now,
      another_value: myTimestamp
  };
  
  await this.collection.add(myData);
  </code></pre>
  
  <p>Any idea how is it possible to create valid <code>UTC</code> Timestamp for Firestore?</p>