Update eslint and eslint-config-cesium

[ggetz]

Description

Following up from CesiumGS/eslint-config-cesium#6, this bumps the version of eslint and corresponding packages. The major change is a migration from .eslintrc.js files to flat config files.

Other notable changes include:

• Added a package.json and corresponding config to .github/actions/check-for-cla. This was mainly to make eslint happy, but is probably better practice anyway to ensure version compatibility with dependencies.
• Removed outdated inline eslint comments where found
• Bumped minimum supported version for compatibility, which matches the current LTS of NodeJS anyway

Issue number and link

N/A

Testing plan

1. Run npm eslint and confirm there are no issues
2. Introduce an eslint error to ensure that errors still surface when running npm eslint.

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• [-] I have updated CHANGES.md with a short summary of my change
• [-] I have added or updated unit tests to ensure consistent code coverage
• [-] I have update the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @ggetz!

✅ We can confirm we have a CLA on file for you.

[jjspace]

@ggetz make-zip is failing for a missing .eslintignore file

[jjspace]

Looks pretty good, just a handful of comments.

I'll also add after actually seeing it in action I still don't think I like this new "flat config". It just seems harder to actually grok and parse what's happening in different parts of the project. but that's just me, no avoiding it if we want to keep up to date.

[ggetz]

@jjspace This should be ready for another look.

[jjspace]

Apparently prettier didn't like that merge but I touched it up quick.

LGTM, thanks @ggetz!