Fabric: Implementation of ViewProps::zIndex feature in C++ core

Summary:
Now, having `orderIndex` feature in the core, we can use it for implementing `zIndex` feature. All we need to do is just to assign this `zIndex` value to `orderIndex`.
Then we will use this to remove some platform-specific code that implements `zIndex` on the mounting layer.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D20432155

fbshipit-source-id: b4d62b63006f45899de38e1f40b1dfbe69550ada

ReactCommon/fabric/components/view/ViewShadowNode.cpp

@@ -11,34 +11,36 @@
 namespace facebook {
 namespace react {
 
-const char ViewComponentName[] = "View";
+char const ViewComponentName[] = "View";
 
 ViewShadowNode::ViewShadowNode(
     ShadowNodeFragment const &fragment,
     ShadowNodeFamily::Shared const &family,
     ShadowNodeTraits traits)
     : ConcreteViewShadowNode(fragment, family, traits) {
-  updateTraits();
+  initialize();
 }
 
 ViewShadowNode::ViewShadowNode(
     ShadowNode const &sourceShadowNode,
     ShadowNodeFragment const &fragment)
     : ConcreteViewShadowNode(sourceShadowNode, fragment) {
-  updateTraits();
+  initialize();
 }
 
-static bool isColorMeaningful(SharedColor const &color) {
+static bool isColorMeaningful(SharedColor const &color) noexcept {
   if (!color) {
     return false;
   }
 
   return colorComponentsFromColor(color).alpha > 0;
 }
 
-void ViewShadowNode::updateTraits() {
+void ViewShadowNode::initialize() noexcept {
   auto &viewProps = static_cast<ViewProps const &>(*props_);
 
+  orderIndex_ = viewProps.zIndex;
+
   bool formsStackingContext = !viewProps.collapsable ||
       viewProps.pointerEvents == PointerEventsMode::None ||
       !viewProps.nativeId.empty() || viewProps.accessible ||
@@ -54,7 +56,7 @@ void ViewShadowNode::updateTraits() {
   formsView = formsView || formsStackingContext;
 
 #ifdef ANDROID
-  // Force `formsStackingContext` trait for nodes which have .
+  // Force `formsStackingContext` trait for nodes which have `formsView`.
   // TODO: T63560216 Investigate why/how `formsView` entangled with
   // `formsStackingContext`.
   formsStackingContext = formsStackingContext || formsView;

ReactCommon/fabric/components/view/ViewShadowNode.h

@@ -33,7 +33,7 @@ class ViewShadowNode final : public ConcreteViewShadowNode<
       ShadowNodeFragment const &fragment);
 
  private:
-  void updateTraits();
+  void initialize() noexcept;
 };
 
 } // namespace react