…layNode, even in slow CALayer rounding type

- Failing to do so will introduce race conditions in which the property was updated on a background thread but main thread has not executed the block that updates the property of the node's layer. During that window, the layer's property is out-of-date and can't be used.
- After this change, ASDisplayNode's cornerRadius is the only source of truth and users must always use it instead of CALayer's.