(Naga) Cooperative Matrix Support

[kvark]

Connections
Blocked by gfx-rs/rspirv#265
Since rspirv fails validation of the product, even though it's correct.

Description
Adding shader support for KHR_cooperative_matrix. Considering a rather simple scope that is portable between Vulkan and Metal.

Testing
Adds tests.

Squash or Rebase?
Rebase.

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.

API choices

SPIRV and Metal have a fine intersection of the cooperative matrix functionality, with some caveats:

• GLSL calls it "coopmat" while Metal has "simdgroup_typeNxY". I decided to go with "coop_mat" since WGSL fairly consistently separates sub-words with an underscore, e.g. "texture_cube".
• SPIRV requires a "use" to be associated with each matrix type. It's one of A/B/Acc. Metal doesn't. The API decision here is to expose it as a "role" being one of the generic parameters of coop_mat.
• SPIRV has OpCooperativeMatrixLoadKHR and OpCooperativeMatrixMulAddKHR as expressions and OpCooperativeMatrixStoreKHR as a statement. Metal has all of them 3 as statements. I figured the arithmetic operation is defined as "a*b + c", which is an expression, and also the inference of the result type is straightforward. The "store" has to be a statement, and it has practically the same signature as "load", which can't trivially infer the result type. So both of them are expressed as statements.
  • the "T" suffix is for transposed load/store. No strong opinion here.
• Metal also has just the multiplication (as opposed to multiply-add). I opted to not expose this, since we can always follow-up if needed.

[cwfitzgerald]

Haven't actually looked in the PR yet, but you should take a look at the presentation about cooperative matrices from the F2F: https://docs.google.com/presentation/d/1wiy3-ar58ah1W9Qc5trd0gG7fwCo93IJ9YCtQoR6W6c/edit?slide=id.g30fc39156ff_0_0#slide=id.g30fc39156ff_0_0 and the dawn design doc https://dawn.googlesource.com/dawn/+/refs/heads/main/docs/dawn/features/subgroup_matrix.md just to make sure things are synced up with upstream.