* Add unit test to test trait collection changes occur during updates are handles correctly
* Remove handling code in ASDataController:updateWithChangeSet. Previous test should fail
* Correctly handle trait collection changes that occur mid-updates
- Currently, when there is a new trait collection, we correctly propagate it to all visible elements. However, since the propagating block is executed on main thread immediately without waiting for the background editing queue of ASDataController, not all elements are updated.
- Then to fix that, we updated ASDataController to handle these changes inside updateWithChangeSet. This works, but it doesn’t address the underlying issue.
- We now delegate the propagating task to ASDataController which schedule a block to its main serial queue after waiting for its background editing queue.
Although we may not want to support this property long-term, there are some usages of it
that are difficult to avoid. Specifically because the complexity it adds is both low,
and contained to a small area of the code that would be easy to remove it, it would be
great to support this.
The usage relates to apps that require the Interop protocol, and are architected to expect
a few methods / protocols being implemented on the UICollectionView class itself. It does
not directly override ASCollectionView behaviors. So hypothetically, it would also work
if it were possible to set ASCollectionView's superclass.
Instead, the app is making its own subclass descend from ASCollectionView and use the interop
APIs, even in environments where there are no ASCellNodes ever returned.
