title: Keep scroll position in ListView when adding new item on top
body: <p>I am using a <code>ListView.builder</code> to render a chat.</p>
  
  <p>The scenario is the following: A user types in a new chat message, when that happens i am storing the new message in state and therefore the <code>itemCount</code> is increased by one. </p>
  
  <p>If i am at the end of the list, I see the new item directly at the top, everything is OK.</p>
  
  <p>However, if I am in the middle of the chat and an item is added, the view scrolls a little bit. How can I disable this behaviour? I guess it kinda makes sense because the scroll offset is still the same <code>double</code> in the <code>ScrollControllers</code> state, but if there is one more item, it looks like it scrolls...</p>
  
  <p>Is there a good way to do this? I guess the manual approach would be to measure the height of the new item and manually set the correct ScrollController offset again.. but meeeh</p>