Summary:
@public
This diff consists of many interdependent changes which support one simple idea: YogaLayoutableShadowNode is now using YGNode children to iterate on them (it previously relied on `ShadowNode::getChildren()`). All other changes are just an unavoidable consequence of that. Hence we don't need to filter child nodes every single time when we do layout anymore! The logic around `clone callback` is also drastically simpler now.
The new approach also implies that `LayoutableShadowNode` and `YogaLayoutableShadowNode` don't use `shared_ptr`s to refer to ShadowNode objects because new relationship does not imply ownership. No more `SharedShadowNode` objects in those two classes.
Reviewed By: mdvacca
Differential Revision: D8796159
fbshipit-source-id: 6f52f92d1826f3eb13b2f8a132c3ea77de155d82
e906d4cdc9