Solari: Scene bindings for environment map light

[JMS55]

Objective

• Setup scene bindings for atmosphere/envmaplight/skybox/etc for solari.
• Using the envmap for lighting will be a future PR.

Solution

AI generated and cleaned up by me.

• Skybox does not need any handling in Solari - opaque main pass will write it after pathtracing. The only exception is that the reference pathtracer will not show the skybox. Imo this is fine, we could always update the pathtracer to show it later if needed.
• Atmosphere uses GeneratedEnvironmentMapLight, and Skybox with lighting uses EnvironmentMapLight. So find one or the other, and extract it to ExtractedEnvironmentMapLight. Then use the underlying cubemap for lighting.
• If more than one camera has different envmaps, use the first one, and warn the user. Per-camera envmap is not currently supported.
• Always sample mip 0 (unfiltered radiance). In the future, we could track path spread and use that to sample other MIPs.
• No infrastructure setup to use an env map as a light source for NEE atm. That can be a followup as well.

Testing

Tested in solari.rs in a future PR that also changes lighting