Fabric: Stopping creating ShadowView instances for non-View ShadowNodes

Summary:
Apparently, the previous behavior brings more problems than some *possible-in-the-future* features and flexibility.
The new model allows us to easily implement "nested text" feature.

(We temporary hope the old behavious for Android only for compatibility reasons.)

Reviewed By: mdvacca

Differential Revision: D13176277

fbshipit-source-id: 01f7bfb3c2e70cc89d76ecb78add016ee91cbd63

React/Fabric/RCTScheduler.mm

@@ -28,6 +28,10 @@ public:
   }
 
   void schedulerDidRequestPreliminaryViewAllocation(SurfaceId surfaceId, ComponentName componentName, bool isLayoutable, ComponentHandle componentHandle) override {
+    if (!isLayoutable) {
+      return;
+    }
+
     RCTScheduler *scheduler = (__bridge RCTScheduler *)scheduler_;
     [scheduler.delegate schedulerOptimisticallyCreateComponentViewWithComponentHandle:componentHandle];
   }

ReactCommon/fabric/uimanager/Differentiator.cpp

@@ -20,7 +20,17 @@ static void sliceChildShadowNodeViewPairsRecursively(
 
     const auto layoutableShadowNode =
         dynamic_cast<const LayoutableShadowNode *>(childShadowNode.get());
+#ifndef ANDROID
+    // New approach (iOS):
+    // Non-view components are treated as layout-only views (they aren't
+    // represented as `ShadowView`s).
+    if (!layoutableShadowNode || layoutableShadowNode->isLayoutOnly()) {
+#else
+    // Previous approach (Android):
+    // Non-view components are treated as normal views with an empty layout
+    // (they are represented as `ShadowView`s).
     if (layoutableShadowNode && layoutableShadowNode->isLayoutOnly()) {
+#endif
       sliceChildShadowNodeViewPairsRecursively(
           pairList,
           layoutOffset + shadowView.layoutMetrics.frame.origin,