[collapsible] onOpenChangeComplete

# Feature request

## Summary

Similar to Dialog and Popover, it would be nice to know when the openChange animation is complete.

## Examples in other libraries

## Motivation

We set `overflow: hidden` during animations so scrollbars don't get shown during the animation. This is causing problems for some components that display popovers using absolute positioning from inside the collapsible container. We would use this prop to set an "isAnimating" prop to conditionally apply the styles we want.

Besides onOpenChangeComplete, another nicer approach would be if the transitionStatus value (and `data-` attributes) could be used to know if an open animation is in-progress. Unfortunately, it seems like transitionStatus is "idle" when the open animation is happening.