* Make ASCellNode indexPath and supplementaryElementKind atomic
* Update the change log
* Fix licenses
* Be explicit with atomic
* Rename the protocol
* And the file
* Fix trait collection handling in ASCollectionElement
- Don't store a trait environment directly and request it when needed. The environment is often the cotaining collection/table node. Asking it for a trait collection is an upward tree traversal and can cause deadlocks. This reverts #2963.
- If the environment changes during a change set update, notify all visible elements about the change. This fixes#2959.
* Address comments
