upgrade to ESLint 9

[nzakas]

This upgrades to ESLint 9 along with switching the .eslintrc.cjs and .eslintignore files to an eslint.config.mjs file.

Note: Due to some of the packages depending strictly on ESLint 8, you'll need to do an npm install -f to force the dependencies to be installed. After that, npm run lint works as expected.

I also updated the lint script in package.json to remove the unnecessary flags.

[barbalex]

Thank you for creating eslint and this pull request!!!!!

Admittedly upgrading eslint to v9 is a bit harder than I would have wished. I tried once, then gave up. Hoping that things would advance and it would become easier with time.
I see you are actively working on just that.