Eslint 9 Upgrade

[rajsite]

Pull Request

🤨 Rationale

Adopts eslint v9 🎉

👩‍💻 Implementation

• Switches to ni eslint config packages using flat config
• Removes prettier-eslint which is in alpha builds for eslint v9 support, significantly hurt lint performance, and had major conflicts with eslint. Now that eslint libraries like stylistic are dedicated to style rules and eslint supports more formats such as markdown syntax and markdown style it's possible we don't need to rely on prettier long term. Either way we remove prettier for now to unblock eslint upgrades and can reconsider in the future
• Linting performance was significantly improved so simplified the validate concurrency scripts to run all lint sequentially in parallel to tests. Now validate completes ~100s faster. It's also possible we will get another speed bump enabling multithreaded eslint but will save for a follow-up PR.
• In the nimble private eslint-config-nimble package:
  • Created a shared lintNimbleConfig configuration that is used in each eslint config to make sure the eslint config file itself is linted and to give a spot for very general shared config in follow-up PRs (like markdown or json linting)
  • Created an angular lint similar to our typescript / component configs as shared config for the angular projects. This resolves issues where extending from a base config in the angular workspace is technically crossing a library boundary and triggered lint errors about reaching across package boundaries. Now we explicitly depend on a shared package.
• Angular workspace changes:
  • The angular workspace root config is now for the config file in root, not the angular projects.
  • Each angular project uses the shared angularTypescriptNimbleConfig and angularTemplateNimbleConfig
• Root workspace changes:
  • Added a top-level eslint config file for the config in root (the config file itself and beachball) but could also be used for linting markdown, etc. in the future.
  • Having a root eslint config also prevents the eslint vscode plugin from getting confused (errors in extension output logs) searching for the eslint config for files in root.

🧪 Testing

Note, see #2774 for CI results and source changes resulting from this config change.

✅ Checklist

• I have updated the project documentation to reflect my changes or determined no changes are needed. A follow-up PR will remove prettier references and docs

[rajsite]

Bypassing other owners for lint only changes