title: Flutter rotate icon on button press with animation
body: <p>I have a <code>button</code> with a <code>icon</code> inside of it. Right now I am using two different <code>icons</code> and change them <code>onTap</code>:</p>
  <pre><code>Widget build(BuildContext context) {
  return GestureDetector(
    onTap: () {
      setState(() {
          _isDropdownOpened = !_isDropdownOpened;
        }
    ...
    },
    child: 
          _isDropdownOpened
              ? SvgPicture.asset(
                  'images/icons/arrow_down_primary.svg',
                  width: scaleWidth(12),
                )
              : SvgPicture.asset(
                  'images/icons/arrow_up_primary.svg',
                  width: scaleWidth(12),
                ),
    ),
  );
  </code></pre>
  <p>This is working but I would like to have a <code>RotationTransition</code>. How can I rotate my <code>icon</code> <code>onTap</code> <strong>with animation</strong>, so I don't need two different SVGs?</p>