title: How to set the time zone in the showDatePickerDialog's DayPicker
body: <p>I'm in need of a DatePickerDialog that's completely handled in UTC (for aviation), ignoring the phone's current time zone. Is it possible to use showDatePickerDialog() and set its DayPicker to UTC, or more specifically: have the current day (which is depicted in the theme's accent color) shown in UTC?</p>
  
  <p>Example:</p>
  
  <p>My phone is set to CET and it's 07-APR-2020 00:30 CET, which without DST is 06-APR-2020 23:30 UTC. I've managed to show the currently selected date on the 6th by using the showDatePicker() function like this:</p>
  
  <pre><code>showDatePicker(
    context: context,
    initialDate: DateTime.now().toUtc(),
    firstDate: DateTime.now().toUtc().subtract(Duration(days: 365)),
    lastDate: DateTime.now().toUtc().add(Duration(days: 90)),
  );
  </code></pre>
  
  <p>but the "current date" in the DayPicker is still in CET, demonstrated in the picture below.</p>
  
  <p><a href="https://i.stack.imgur.com/4WDFa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4WDFa.png" alt="enter image description here"></a></p>
  
  <p>Is there any way to change that so it uses the UTC value for the current date?</p>