Update shader bencher to share some logic with snapshots

[SupaMaggie70Incorporated]

Connections
This is to address test failings in #7930 due to not respecting supported backends. In fact, its pulled directly from the last few commits there.

Description
Previously, the shader bencher was using snapshot shaders but not respecting their options, such as which backends they should be tested against. As a result, in #7930, a mesh shader test shader that only can be written to SPIRV was causing the shader bencher to fail. I have updated the shader bencher and snapshots to share more logic.

See this comment

Testing
The change is to testing itself. I have verified that the bencher still fails on bad shader inputs, and that it ignores my mesh shader as it is supposed to.

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.