[Presence] Ensure onAnimationEnd when closing

[YarnSphere]

Make sure that onAnimationEnd is fired for consumers, after the closing animation of a component.

Fixes: #1020

I hit #1020 when implementing an imperative API over toasts, where I want to remove a toast from the list of open toasts after it finishes its "close" animation. I expect wanting to know when an element finishes closing to be a relatively common need.

[YarnSphere]

A completely different approach to solving #1020 would be to change the Presence component to receive an extra property onAnimationEnd (the same event handler that would otherwise have been passed to the component we are animating) and manually call onAnimationEnd before we call flushSync.

This would require going through every usage of Presence in Radix and pass it the onAnimationEnd handler that was being passed to the animating component.

The biggest downside of this approach (besides the fact that we're complicating Presence) is that we'd have mismatched signatures for onAnimationEnd, since we're dealing with "real" events here, rather than synthetic ones, so we'd likely have to deal with that discrepancy somehow.

What are your thoughts? Do you have any other ideas on how to solve this? I'm leaving this PR here with this possible solution, but am happy to change the approach if you find it inadequate.