title: Animate intrinsicContentSize changes
body: <p>I have a UIView subclass that draws a circle whose radius changes (with nice bouncy animations). The view is deciding the size of the circle.</p>
  
  <p>I want this UIView subclass to change its frame size to match the animated changes to the circle radius, and I want these changes to modify any NSLayoutConstraints connected to the view (so that views that are constrained to the edge of the circle will move as the circle resizes).</p>
  
  <p>I understand that implementing <code>-(CGSize)intrinsicContentSize</code> and calling <code>invalidateIntrinsicContentSize</code> when the radius changes will tell constraints to update, but I cant figure out how to animate the changes to <code>intrinsicContentSize</code>. </p>
  
  <p>Calling <code>invalidateIntrinsicContentSize</code> from within a [UIView animateWith... block just instantly updates the layout.</p>
  
  <p>Is this even possible, and is there a workaround/better approach?</p>