Fabric: Using `traitCast` in UIManager

Summary:
This is another perf-critical place where using traitCast should help with perf.
After this change we practically will not have any `dynamic_cast`s (except those which will be delited (with methods where they are used) in the future diffs).

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D20052029

fbshipit-source-id: 63b589d3c3322f0afd72f18b4701fe31d0e05c2f

ReactCommon/fabric/uimanager/UIManager.cpp

@@ -176,9 +176,9 @@ LayoutMetrics UIManager::getRelativeLayoutMetrics(
   }
 
   auto layoutableShadowNode =
-      dynamic_cast<const LayoutableShadowNode *>(&shadowNode);
+      traitCast<LayoutableShadowNode const *>(&shadowNode);
   auto layoutableAncestorShadowNode =
-      dynamic_cast<const LayoutableShadowNode *>(ancestorShadowNode);
+      traitCast<LayoutableShadowNode const *>(ancestorShadowNode);
 
   if (!layoutableShadowNode || !layoutableAncestorShadowNode) {
     return EmptyLayoutMetrics;