Fabric: More asserts in YogaLayoutableShadowNode

Summary:
These `assert`s must be satisfied. Having them allows us to fail early in case of bugs.
I spent a log of time debugging an issue and finally found that after adding those `assert`s.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: mdvacca

Differential Revision: D20268046

fbshipit-source-id: 1d8ddd6de00069bd2a79e74af5e4278aa6c9131b

Author: shergin

ReactCommon/fabric/components/view/yoga/YogaLayoutableShadowNode.cpp

@@ -261,11 +261,15 @@ void YogaLayoutableShadowNode::layoutTree(
 }
 
 void YogaLayoutableShadowNode::layoutChildren(LayoutContext layoutContext) {
+  assert(!yogaNode_.isDirty());
+
   for (const auto &childYogaNode : yogaNode_.getChildren()) {
     if (!childYogaNode->getHasNewLayout()) {
       continue;
     }
 
+    assert(!childYogaNode->isDirty());
+
     auto childNode =
         static_cast<YogaLayoutableShadowNode *>(childYogaNode->getContext());