GatherVisibleLightsGPU Move depth prepass to be the first pass of everything, we'll use it on lightbinner for light culling from now on Do lightbinning for light culling on render thread when a layer first wants to request lights, guarantees we have a depth pyramid by then If we are on a render thread just do a simple flush for ForceFlushGPU(), we just want the GPU to finish it's work, not clean up things