feat(srp): add shader pass selection for scene draws

- let DrawingSettings carry an optional shaderPassName across managed and native scene draw APIs
- allow RenderObjectsRendererFeature to author explicit ForwardLit or Unlit scene draws
- exercise the new scene draw pass selection seam in the project render pipeline probe

managed/XCEngine.ScriptCore/InternalCalls.cs

@@ -782,7 +782,8 @@ namespace XCEngine
                 ulong nativeHandle,
                 int scenePhase,
                 ref Rendering.RendererListDesc rendererListDesc,
-                string overrideMaterialPath);
+                string overrideMaterialPath,
+                string shaderPassName);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern bool