Summary:
Adds a factory method to `YogaNode`.
While this is purely redundant at the moment, it will allow experimentation in follow-up diffs. We will have concrete implementations deriving from `YogaNode` (which will be abstract).
Going through `YogaNode.create()` means that we can maintain ABI compatibility.
Reviewed By: amir-shalem
Differential Revision: D14122974
fbshipit-source-id: 15d92f296d91cc8bbd79a196f370d2dbb69b3f92