ESLint v9 migration

[ttsukagoshi]

See:

• Migrate to v9.x - ESLint - Pluggable JavaScript Linter
• Flat config rollout plans - ESLint - Pluggable JavaScript Linter

[ttsukagoshi]

This will be a major version update since it requires changes to the ESLint configuration file eslintrc and Node.js requirements in package.json

[ttsukagoshi]

Migration will move forward once the public version of typescript-eslint v8, with full support for eslint v9, is released.