feat!: stricter validation of rule tests

[bmish]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[X] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Adds rule test assertions per eslint/rfcs#84
Fixes #15104

This demonstrates the changes needed for this RFC.

TODO:

• Wait for RFC approval
• Wait for ESLint v9
• Add tests

Is there anything you'd like reviewers to focus on?

[eslint-github-bot]

Hi @bmish!, thanks for the Pull Request

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[nzakas]

@bmish given that v9 is pretty far away, would you mind if we closed this PR? You can obviously continue to work on the branch, but right now it’s just noise in the list of PRs. You can always reopen when we are closer to v9

[bmish]

@nzakas yep totally fine.