Simplify bitfields (#1393)

Summary:
X-link: https://github.com/facebook/react-native/pull/39485

Pull Request resolved: https://github.com/facebook/yoga/pull/1393

These were previously packed into structs to allow zero initializing all the flags at once without needing a ctor. C++ 20 has in-class member initializer support for bitfields, which makes these look more like normal member variables.

Setting enum values is a bit jank right now, due to relying on C enums which are effectively int32_t, along with GCC `-Wconversion` being a bit aggressive in needing to explicitly mask. I have some ideas to fix this later (e.g. using scoped enums internally).

bypass-github-export-checks

Changelog:
[General][Breaking] - Require C++ 20 when including renderer headers

Reviewed By: sammy-SC

Differential Revision: D49265967

fbshipit-source-id: 6ab935a866196df06e742c821f3af88eb4d18e1a

yoga/node/Node.h

@@ -26,20 +26,13 @@ struct YGNode {};
 
 namespace facebook::yoga {
 
-#pragma pack(push)
-#pragma pack(1)
-struct NodeFlags {
-  bool hasNewLayout : 1;
-  bool isReferenceBaseline : 1;
-  bool isDirty : 1;
-  NodeType nodeType : bitCount<NodeType>();
-};
-#pragma pack(pop)
-
 class YG_EXPORT Node : public ::YGNode {
  private:
+  bool hasNewLayout_ : 1 = true;
+  bool isReferenceBaseline_ : 1 = false;
+  bool isDirty_ : 1 = false;
+  NodeType nodeType_ : bitCount<NodeType>() = NodeType::Default;
   void* context_ = nullptr;
-  NodeFlags flags_ = {};
   YGMeasureFunc measureFunc_ = {nullptr};
   YGBaselineFunc baselineFunc_ = {nullptr};
   YGPrintFunc printFunc_ = {nullptr};
@@ -92,11 +85,11 @@ class YG_EXPORT Node : public ::YGNode {
   void print();
 
   bool getHasNewLayout() const {
-    return flags_.hasNewLayout;
+    return hasNewLayout_;
   }
 
   NodeType getNodeType() const {
-    return flags_.nodeType;
+    return nodeType_;
   }
 
   bool hasMeasureFunc() const noexcept {
@@ -142,7 +135,7 @@ class YG_EXPORT Node : public ::YGNode {
   }
 
   bool isReferenceBaseline() const {
-    return flags_.isReferenceBaseline;
+    return isReferenceBaseline_;
   }
 
   // returns the Node that owns this Node. An owner is used to identify
@@ -175,7 +168,7 @@ class YG_EXPORT Node : public ::YGNode {
   }
 
   bool isDirty() const {
-    return flags_.isDirty;
+    return isDirty_;
   }
 
   std::array<YGValue, 2> getResolvedDimensions() const {
@@ -250,11 +243,11 @@ class YG_EXPORT Node : public ::YGNode {
   }
 
   void setHasNewLayout(bool hasNewLayout) {
-    flags_.hasNewLayout = hasNewLayout;
+    hasNewLayout_ = hasNewLayout;
   }
 
   void setNodeType(NodeType nodeType) {
-    flags_.nodeType = nodeType;
+    nodeType_ = nodeType;
   }
 
   void setMeasureFunc(YGMeasureFunc measureFunc);
@@ -280,7 +273,7 @@ class YG_EXPORT Node : public ::YGNode {
   }
 
   void setIsReferenceBaseline(bool isReferenceBaseline) {
-    flags_.isReferenceBaseline = isReferenceBaseline;
+    isReferenceBaseline_ = isReferenceBaseline;
   }
 
   void setOwner(Node* owner) {