Cleanup YGNode for explicit per-node config

Summary:
Cleans up some of the changes to UseWebDefaults that were made in the interest of moving it outside of YGConfig. It still exists in YGConfig, but also exists on the node.

We also assert on null config, or when someone tries to change UseWebDefaults after creating a node (since right now YGStyle does not know the difference between unset vs set explicitly to what would normally be default).

Removes a peculiar constructor which was added to avoid config setting.

Reviewed By: rshest

Differential Revision: D45133644

fbshipit-source-id: 2b5e2baeb826653133df9b1175cf5c194e342e3e

yoga/YGNode.h

@@ -29,7 +29,6 @@ struct YGNodeFlags {
   bool measureUsesContext : 1;
   bool baselineUsesContext : 1;
   bool printUsesContext : 1;
-  bool useWebDefaults : 1;
 };
 #pragma pack(pop)
 
@@ -72,7 +71,6 @@ private:
   void setBaselineFunc(decltype(baseline_));
 
   void useWebDefaults() {
-    flags_.useWebDefaults = true;
     style_.flexDirection() = YGFlexDirectionRow;
     style_.alignContent() = YGAlignStretch;
   }
@@ -87,14 +85,8 @@ private:
   using CompactValue = facebook::yoga::detail::CompactValue;
 
 public:
-  YGNode() : YGNode{YGConfigGetDefault()} {}
-  explicit YGNode(const YGConfigRef config) : config_{config} {
-    flags_.hasNewLayout = true;
-
-    if (config->useWebDefaults) {
-      useWebDefaults();
-    }
-  };
+  YGNode() : YGNode{YGConfigGetDefault()} { flags_.hasNewLayout = true; }
+  explicit YGNode(const YGConfigRef config);
   ~YGNode() = default; // cleanup of owner/children relationships in YGNodeFree
 
   YGNode(YGNode&&);
@@ -103,8 +95,9 @@ public:
   // Should we remove this?
   YGNode(const YGNode& node) = default;
 
-  // for RB fabric
-  YGNode(const YGNode& node, YGConfigRef config);
+  [[deprecated("Will be removed imminently")]] YGNode(
+      const YGNode& node,
+      YGConfigRef config);
 
   // assignment means potential leaks of existing children, or alternatively
   // freeing unowned memory, double free, or freeing stack memory.
@@ -300,7 +293,7 @@ public:
 
   // TODO: rvalue override for setChildren
 
-  void setConfig(YGConfigRef config) { config_ = config; }
+  void setConfig(YGConfigRef config);
 
   void setDirty(bool isDirty);
   void setLayoutLastOwnerDirection(YGDirection direction);