Fabric: Enabling view hierarchy flattening (for <View> component only for now)

Summary: This change implements `onLayoutOnly` for regular bare <View> component (*not* for its descendants!) After this view flattening is actually starting working for all platforms.

Reviewed By: mdvacca

Differential Revision: D9511001

fbshipit-source-id: 3562dd1b7570a064150f100cc2e1bc4220b81290

ReactCommon/fabric/components/view/ViewShadowNode.cpp

@@ -12,5 +12,32 @@ namespace react {
 
 const char ViewComponentName[] = "View";
 
+bool ViewShadowNode::isLayoutOnly() const {
+#ifdef ANDROID
+  // This feature is not properly tested on Android yet.
+  return false;
+#else
+  const auto &viewProps = *std::static_pointer_cast<const ViewProps>(props_);
+
+  return
+    // Event listeners
+    !viewProps.onLayout &&
+    // Generic Props
+    viewProps.nativeId.empty() &&
+    // Accessibility Props
+    !viewProps.accessible &&
+    // Style Props
+    viewProps.yogaStyle.overflow == YGOverflowVisible &&
+    viewProps.opacity == 1.0 &&
+    !viewProps.backgroundColor &&
+    !viewProps.foregroundColor &&
+    !viewProps.shadowColor &&
+    viewProps.transform == Transform {} &&
+    viewProps.zIndex == 0 &&
+    // Layout Metrics
+    getLayoutMetrics().borderWidth == EdgeInsets {};
+#endif
+}
+
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/components/view/ViewShadowNode.h

@@ -15,12 +15,21 @@ namespace react {
 
 extern const char ViewComponentName[];
 
-using ViewShadowNode =
-  ConcreteViewShadowNode<
+/*
+ * `ShadowNode` for <View> component.
+ */
+class ViewShadowNode final:
+  public ConcreteViewShadowNode<
     ViewComponentName,
     ViewProps,
     ViewEventEmitter
-  >;
+  > {
+
+public:
+  using ConcreteViewShadowNode::ConcreteViewShadowNode;
+
+  bool isLayoutOnly() const;
+};
 
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/components/view/accessibility/AccessibilityProps.h

@@ -29,7 +29,7 @@ public:
 
 #pragma mark - Props
 
-  const bool accessible {true};
+  const bool accessible {false};
   const std::vector<std::string> accessibilityActions {};
   const std::string accessibilityLabel {""};
   const AccessibilityTraits accessibilityTraits {AccessibilityTraits::None};