Migrate to ESM

[nix6839]

To give the community time to migrate to ESM, we'll publish a hybrid package to support the (now deprecated) CommonJS Node.js API until our next major release.
-- https://stylelint.io/migration-guide/to-16

There was an error about ESM in Jest, so I used jest-light-runner.

[kristerkari]

Thanks!

Migrating to ESM is a major breaking change, so my thinking is that the ESM migration would be better done after stylelint has fully migrated to ESM.

[nix6839]

Thanks!

Migrating to ESM is a major breaking change, so my thinking is that the ESM migration would be better done after stylelint has fully migrated to ESM.

When the time comes, please ping me. Until then, I'll periodically rebase :)