Fixes#44424 by adding the `app` folder to an `ESLINT_DEFAULT_DIRS`
constant which defines all folders where the linter should go through.
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
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Co-authored-by: JJ Kasper <jj@jjsweb.site>
Fixes#38533 by including `src/` as a default linting directory where all files within are linted
## Bug
- [X] Related issues linked using `fixes #number`
- [X] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`