EffectComposer: Add option for custom render pass

[shotamatsuda]

I've been trying MRT with EffectComposer in order to avoid additional render passes to output normals, masks, and so on. Extensibility is always a problem with pure components, but in this case, having a RenderPass prop in EffectComposer to accept a class implementing the same interface as RenderPass would allow us to use a custom render pass. Otherwise, and this is my current workaround, we must maintain a modified copy of EffectComposer, which is suboptimal in terms of maintainability.

Like:

export const EffectComposer = memo(
  forwardRef<EffectComposerImpl, EffectComposerProps>(
    (
      {
        ...,
        RenderPass = RenderPass
      },
      ref
    ) => {
      ...
      const [composer, normalPass, downSamplingPass] = useMemo(() => {
        ...
        // Add render pass
        effectComposer.addPass(new RenderPass(scene, camera))
        ...
      }, [
        ...,
        RenderPass
      ])
      ...
    }
  )
)

I'd like to hear your opinion.