[Fix] Clustered lighting correctly supports light layers

[mvaligursky]

Fixes #4791

• instead of using all lights for clusters, only a set of lights used by the layer is used.

[willeastcott]

Approving although slightly concerned about the forEach call. I tend to avoid those within the render loop because forEach is like an order of magnitude slower than a for loop (he says without the supporting data to hand).

[mvaligursky]

Yeah I agree, but the data is stored in a Set and forEach is the only way to iterate it. I could maintain a dirty flag and update an array if Set changes, but I suspect this could be fine for just lights doing a single loop over those per frame.