refactor(srp): move directional shadow planning policy into managed urp

engine/include/XCEngine/Rendering/Pipelines/ManagedScriptableRenderPipelineAsset.h

@@ -107,6 +107,10 @@ public:
         (void)rendererIndex;
         return GetCameraFrameStandalonePassAssetKey(stage);
     }
+    virtual std::string GetDirectionalShadowPlanningPolicyAssetKey()
+        const {
+        return {};
+    }
     virtual std::string GetDirectionalShadowExecutionPolicyAssetKey()
         const {
         return {};