refactor(srp): move universal shadow ownership into asset layer

- track missing render graph scriptcore sources and rendering utility headers

- expose camera request directional shadow control to managed universal asset configuration

managed/XCEngine.ScriptCore/Rendering/Graph/RenderGraphTextureHandle.cs

@@ -0,0 +1,30 @@
+namespace XCEngine.Rendering
+{
+    public struct RenderGraphTextureHandle
+    {
+        private readonly int m_indexPlusOne;
+
+        private RenderGraphTextureHandle(
+            int indexPlusOne)
+        {
+            m_indexPlusOne = indexPlusOne;
+        }
+
+        public bool isValid =>
+            m_indexPlusOne > 0;
+
+        internal int nativeIndex =>
+            m_indexPlusOne > 0
+                ? m_indexPlusOne - 1
+                : -1;
+
+        internal static RenderGraphTextureHandle
+        FromNativeIndex(int nativeIndex)
+        {
+            return nativeIndex >= 0
+                ? new RenderGraphTextureHandle(
+                    nativeIndex + 1)
+                : default;
+        }
+    }
+}