Initial naga changes for mesh shaders

[SupaMaggie70Incorporated]

Connections
#7197

Description
This PR isn't meant to be merged itself, its obviously way too large for that. Instead I will be breaking off chunks into separate PRs.

Testing
There is a test WGSL shader that is parsed and then written to SPIR-V

Squash or Rebase?
Absolutely squash

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

[SupaMaggie70Incorporated]

@andyleiserson Preferably I would want the toml configuration logic to be shared and not copy/pasted between different crates. But I am not familiar enough with the project structure to know where it should live, or if the naga benchmarks should be moved to the crate in naga/tests/naga. So if you or someone else could provide an opinion about how to handle that I'd be happy to do the leg work (probably in a separate PR).

That being said, I get the impression that refactors of code/moving code around should only be done by trusted people, as other individuals could hide something malicious in the large change. Not sure about wgpu's process in that regard but something to keep in mind probably.

[cwfitzgerald]

This is an absolutely herculean effort! I didn't see much that is would be of major concern.

I would advise however splitting up the PR, either into multiple PRs or multiple independent commits. A possible suggestion for splitting

• IR changes + ron test output changes
• WGSL frontend
• Spirv backend

The wgsl frontend and spirv backend could be completely independent PRs, both dependent on the fairly minor IR changes. I think that would put diff sizes in the more reasonable range.

[cwfitzgerald]

This could use a number of comments explaining what we're doing here and why we need to do it for mesh shaders. This is a very long and important function, so comments throughout explaining it all (will also help).

[SupaMaggie70Incorporated]

I attempted to write some comments. Let me know if you think I should do more.

[SupaMaggie70Incorporated]

@cwfitzgerald Thanks for the review. I've tried to sprinkle a few more comments around the code in addition to addressing your comments, so if you could ensure that the code is understandable to yourself and others that would be great. Your idea for splitting up the PR is pretty much exactly what I was thinking. I will probably break off the naga IR changes tomorrow. I'll also hopefully find the motivation to fix the benchmark issue before WGSL parsing gets merged in.