Main point was to enable ESLint `dot-notation` and `no-unneeded-ternary`
rules for more code consistency.
I took the occasion to add two minor commits:
- Fix a problem found by running `test:spelling
- Minor dependency update
It wouldn't be a problem if the PR didn't arrive in the next release,
the changes are cosmetic.
Since PR #3551 was not yet complete, I made my own attempt.
1. Update to ESLint v9.
2. Replace deprecated `.eslintrc.json` and `.eslintignore` by flat
config `eslint.config.mjs`.
3. Adapt `check_config.js` to use flat config.
4. Since `eslint-plugin-import` still doesn't support ESLint v9 I
removed it. We can add it back when it does support v9.
5. Run tests `npm run check:js` and `npm run config:check`.
6. In order not to overload this PR, I have not yet activated more
additional rules - there are some useful ones in the new plugin
`@eslint/js`.
@bugsounet, please don't take it as an offence that I have created a
competing PR. The migration to ESLint v9 has been burning under my nails
for some time.