introduce ShadowNode::IdentityTrait (#41603)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41603

changelog: [internal]

`ShadowNode::IdentityTrait` was already a thing. Let's make it available in ConcreteComponentDescriptor.

Reviewed By: rshest

Differential Revision: D51471666

fbshipit-source-id: 7919a9b7238d766ee3913a5ab239bf254fab0996

packages/react-native/ReactCommon/react/renderer/core/ConcreteShadowNode.h

@@ -70,6 +70,10 @@ class ConcreteShadowNode : public BaseShadowNodeT {
     return BaseShadowNodeT::BaseTraits();
   }
 
+  static ShadowNodeTraits::Trait IdentifierTrait() {
+    return BaseShadowNodeT::IdentifierTrait();
+  }
+
   static UnsharedConcreteProps Props(
       const PropsParserContext& context,
       const RawProps& rawProps,

packages/react-native/ReactCommon/react/renderer/core/ShadowNode.h

@@ -59,6 +59,10 @@ class ShadowNode : public Sealable,
     return ShadowNodeTraits{};
   }
 
+  static ShadowNodeTraits::Trait IdentifierTrait() {
+    return ShadowNodeTraits::Trait::None;
+  }
+
 #pragma mark - Constructors
 
   /*