Occlusion culling via occulsion queries

[expenses]

Using occlusion queries for culling is an Old Skool technique (it's mentioned in GPU Gems which came out over 18 years ago!!).

While we'd ideally be using a depth pyramid for occlusion culling, that's not an option until WebGPU comes out (ideally with an extension that let's us use the right sampler). So this is probably something we should implement at some point (after frustum culling).

The path of least resistance here is probably just to copy BabylonJS here: https://github.com/BabylonJS/Babylon.js/blob/4b074f9f74f25d51edbfc480e1da678cbb5eff8d/packages/dev/core/src/Engines/WebGPU/webgpuOcclusionQuery.ts.