Avoid redundant dynamic_pointer_cast in YogaLayoutableShadowNode clone (#57019)

Summary:
Pull Request resolved: #57019

The clone constructor of `YogaLayoutableShadowNode` rebuilt the
internal `yogaLayoutableChildren_` vector on every clone by
walking every child with `dynamic_pointer_cast`. When the cloned
node inherits its children list from the source (`!fragment.children`)
the result is identical to the source's vector, so copy it directly
instead — no RTTI required.

Also `reserve()` the vector to its upper bound at the top of
`updateYogaChildren()` so the rebuild on the new-children path no
longer reallocates as it grows.

Both changes are pure CPU-time optimizations on a hot path that
shows up heavily in animation-driven tree clones; behaviour is
unchanged.

Changelog:
[Internal]

Reviewed By: christophpurrer, lenaic

Differential Revision: D106287171

fbshipit-source-id: 33efd873fe4e24d91cea69fde650139bc8a89e1e

Author: javache

packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp

@@ -114,11 +114,19 @@ YogaLayoutableShadowNode::YogaLayoutableShadowNode(
       "Yoga node must inherit dirty flag.");
 #endif
   if (!getTraits().check(ShadowNodeTraits::Trait::LeafYogaNode)) {
-    for (auto& child : getChildren()) {
-      if (auto layoutableChild =
-              std::dynamic_pointer_cast<const YogaLayoutableShadowNode>(
-                  child)) {
-        yogaLayoutableChildren_.push_back(std::move(layoutableChild));
+    if (!fragment.children) {
+      // Children unchanged - copy the filtered list directly from the source
+      // node, avoiding expensive dynamic_pointer_cast on every child.
+      yogaLayoutableChildren_ =
+          static_cast<const YogaLayoutableShadowNode&>(sourceShadowNode)
+              .yogaLayoutableChildren_;
+    } else {
+      for (auto& child : getChildren()) {
+        if (auto layoutableChild =
+                std::dynamic_pointer_cast<const YogaLayoutableShadowNode>(
+                    child)) {
+          yogaLayoutableChildren_.push_back(std::move(layoutableChild));
+        }
       }
     }
   }
@@ -349,6 +357,7 @@ void YogaLayoutableShadowNode::updateYogaChildren() {
 
   yogaNode_.setChildren({});
   yogaLayoutableChildren_.clear();
+  yogaLayoutableChildren_.reserve(getChildren().size());
 
   for (size_t i = 0; i < getChildren().size(); i++) {
     if (auto yogaLayoutableChild =