experiment with first-level batching using object index instead of spatial hash in uniform grid (to avoid tuning average object size for uniform grid)

Demos3/GpuDemos/rigidbody/GpuRigidBodyDemo.cpp

@@ -119,6 +119,7 @@ void	GpuRigidBodyDemo::initPhysics(const ConstructionInfo& ci)
 
 		setupScene(ci);
 
+		m_data->m_rigidBodyPipeline->writeAllInstancesToGpu();
 		np->writeAllBodiesToGpu();
 		bp->writeAabbsToGpu();