Implement subgroup quad ops

[dzamkov]

Connections
Partially solves #5555
Resolves #5670

Description
Resurrecting #5684, which implements WGSL's (now accepted) quad operations:

• Rebased onto trunk
• Made QuadSwap operations an instance of SubgroupGather, simplifying the code
• Cleaning up unused code
• Fix to Vulkan backend

Testing

• Added Naga snapshot tests for quad operations
• Integrated into personal project and verified quad operations are working as expected (Vulkan backend only)

Squash or Rebase?

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.