Summary:
@public
Here, we extract an abstract class from `YogaNode`, in order to allow for experimentation with different implementations.
The reason for not choosing an interface is to keep ABI compatibility for `YogaNode.create()`.
Reviewed By: pasqualeanatriello
Differential Revision: D14044990
fbshipit-source-id: f8eb246338b55f34f0401198c0655abfcb7c9f37