Connections
Initial proposal for the wgsl front-end of #6760

Description
Adds wgsl-in and (partial) validation for the simplest version of ray tracing pipelines. This matches the spirv and hlsl specs to the best of my knowledge (though with less than complete validation). Things may change in the future though. @JMS55 may wish to check the naming ect. I don't normally open a naga PR w/o a full way through, but last time I tried pipelines I did that and struggled to keep it up to date.

Naming differences from vulkan
LaunchId -> ray_invocation_id (I think its clearer what it is talking about)
LaunchSize -> num_ray_invocations
InstanceCustomIndex -> instance_custom_data (like ray queries)
RayTmax -> ray_t_current_max (unlike RayTmin, it changes over the life cycle of the ray, and doesn't match the field of the ray desc)

Testing
Snapshot test from wgsl to IR.

Squash or Rebase?
Squash

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests.
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.