Refactor check_workgroup_sizes into a new struct WorkgroupSizeCheck

[ErichDonGubler]

Connections

Done while working on #9732.

Conflicts with #9732. I have a resolution ready in trunk...erichdongubler-mozilla:wgpu:erichdongubler-push-uovkovyvxuzq to handle this.

Description

I think this tidies this bit of code nicely. Recommended review experience is commit-by-commit.

Testing

Things still compile, so I think the risk of something breaking is low.

Squash or Rebase? rebaseplz

Checklist

• I self-reviewed and fully understand this PR.
• WebGPU implementations built with wgpu may be affected behaviorally.
• Validation and feature gates are in place to confine behavioral changes.
• Tests demonstrate the validation and altered logic works.
• CHANGELOG.md entries for the user-facing effects of this change are present.
• The PR is minimal, and doesn't make sense to land as multiple PRs.
• Commits are logically scoped and individually reviewable.
• The PR description has enough context to understand the motivation and solution implemented.