title: Splash Animation on Icon Button is always behind the Stack
body: <p>i'm getting a bug where button click animation always show behind the stack</p>
  <p>bottomNavigationBar: Stack(
  children: [
  BottomNavigationBar(
  type: BottomNavigationBarType.fixed,
  items: [
  BottomNavigationBarItem(...),
  BottomNavigationBarItem(...),
  BottomNavigationBarItem(...),
  // Imitate an invisible icon
  BottomNavigationBarItem(
  icon: const Icon(Icons.add_circle, size: 0),
  title: const Text(''),
  ),
  ],
  currentIndex: _selectedIndex,
  fixedColor: Colors.indigo,
  onTap: _onItemTapped,
  iconSize: 24,
  ),
  Positioned(
  right: 32.0,
  top: 8.5,
  child: CircleAvatar(
  child: IconButton(
  splashColor: Colors.green,
  icon: Icon(Icons.add),
  onPressed: () {},
  ),
  ),
  )
  ],
  ),<a href="https://i.stack.imgur.com/ZGvIx.gif" rel="nofollow noreferrer">enter image description here</a></p>