Use ESM config file for Rollup

[benmccann]

Unfortunately, can't convert the Karma config until Karma 7: karma-runner/karma#3679 (comment)

[LeeLenaleee]

@benmccann the tests are currently failing because karma can't import the rollup config anymore, tried switching to dynamic imports that should work, but can't get it to work, can you take a look at it?

Edit:
Sorry for the mention, seems I finally found the thing I kept overlooking

Fix for failing tests is bundled with the removal of the deatroy hook in #10549

[dangreen]

@kurkle @benmccann karma config imports rollup config, so now it can't be imported and CI falls with error

https://github.com/chartjs/Chart.js/runs/7690926110?check_suite_focus=true

I think need to revert this.

[benmccann]

@dangreen see the comment just above yours: #10564 (comment). The fix is included in #10549. Hopefully we can merge that one soon

[kurkle]

Merged