Migrate eslint config to 9.x

[nhsd-david-wass]

Summary

• Routine Change
• ❗ Breaking Change
• 🤖 Operational or Infrastructure Change
• ✨ New Feature
• ⚠️ Potential issues that might be caused by this change

Add any other relevant notes or explanations here. Remove this line if you have nothing to add.

Reviews Required

• Dev
• Test
• Tech Author
• Product Owner

Review Checklist

ℹ️ This section is to be filled in by the reviewer.

• I have reviewed the changes in this PR and they fill all or part of the acceptance criteria of the ticket, and the code is in a mergeable state.
• If there were infrastructure, operational, or build changes, I have made sure there is sufficient evidence that the changes will work.
• I have ensured the changelog has been updated by the submitter, if necessary.

[francisco-videira-nhs]

A couple of questions:

1. I wonder if we can delete the .eslintrc.js now?
2. Was the new config file created via the migration tool? (I left a comment with more detail in the file.)
3. I wonder if it's worth doing some manual testing by perhaps changing in some files and checking if the linter is working as expected, as this won't otherwise be tested?

[francisco-videira-nhs]

I wonder if this was created via npx @eslint/migrate-config .eslintrc.json? I got a different result on my end. But seems to be fairly similar. I got a eslint.config.js (as opposed to .mjs)

const {
    defineConfig,
} = require("eslint/config");

const globals = require("globals");

module.exports = defineConfig([{
    languageOptions: {
        globals: {
            ...globals.commonjs,
            ...globals.node,
            "Atomics": "readonly",
            "SharedArrayBuffer": "readonly",
        },

        "ecmaVersion": 2018,
        parserOptions: {},
    },

    "extends": "eslint:recommended",
    "rules": {},
}]);

[francisco-videira-nhs]

Looks good. Just a minor comment on commented out lines.

[francisco-videira-nhs]

Wondering if these can be taken out?

[francisco-videira-nhs]

Approved.