Naga mesh shader WGSL writer

[Slightlyclueless]

Connections
Based off of #8370

Description

Adds a WGSL writer for mesh shader functionality.

Testing
TODO

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.

[inner-daemons]

Thumbs up from me, no further comments

[cwfitzgerald]

Ci is mad

[cwfitzgerald]

Looks good, some comments

[Slightlyclueless]

uhhh, that's not any of my code causing CI to get mad...

[Copilot]

Pull request overview

This PR adds WGSL writer support for mesh shader functionality to Naga, building on PR #8370 which added the parsing support. The implementation enables round-trip conversion of mesh shader code through the WGSL writer, completing the mesh shader support for WGSL.

Key Changes

• Added WGSL writer support for mesh and task shader stages with proper attribute handling (@mesh, @task, @payload)
• Implemented built-in name mappings for mesh shader-specific built-ins (mesh_task_size, triangle_indices, etc.)
• Added support for task_payload address space and per_primitive attribute in WGSL output
• Updated test targets from "IR | ANALYSIS" to "WGSL" to generate WGSL output files instead

Reviewed changes

Copilot reviewed 7 out of 23 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
naga/src/common/wgsl/to_wgsl.rs	Exposed mesh shader built-in names (previously returned None) and added task_payload address space string
naga/src/back/wgsl/writer.rs	Added MeshStage, TaskPayload, and PerPrimitive attribute variants; implemented mesh/task entry point attribute handling; added wgpu_mesh_shader enable detection
naga/tests/in/wgsl/*.toml	Changed test targets from "IR | ANALYSIS" to "WGSL"
naga/tests/out/wgsl/*.wgsl	New WGSL output files for mesh shader test cases
naga/tests/out/ir/*.ron	Removed IR output files (no longer generated)
naga/tests/out/analysis/*.info.ron	Removed analysis output files (no longer generated)
CHANGELOG.md	Added entry documenting the new WGSL writer support

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[cwfitzgerald]

That's it? Hell yeah