Replace deprecated babel-polyfills in favor of core-js and regenerator-runtime

[tleunen]

Description

Babel-polyfill is deprecated and shouldn't be used anymore. We should use core-js directly now.
https://babeljs.io/docs/en/babel-polyfill

I'm aware of this issue that cause the revert somehow. But I think it was caused by a misconfiguration maybe? By using core-js v3. We should also update our babel preset to configure preset-env with corejs 3, and might prevent the size increase?

Currently, we still default on v2, but consumers can customize it. Once this PR is shipped, we should default on v3. https://github.com/Shopify/web-configs/blob/ba2c02cac3fc150c5603493506e7115774335e59/packages/babel-preset/web.js#L6

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above (Documentation fix and Test update does not need a changelog as we do not publish new version)

[ismail-syed]

Why isn't v3 begin reflected in the yarn.lock 🤔

[tleunen]

Probably because other packages use v2? I haven't really looked much into that as it seems upgrading to v3 is more problematic than I thought

[ismail-syed]

Would this be a breaking change or minor?

[tleunen]

I think it would actually be a major since it requires consumers to run babel with the corejs v3 flag. But @alexandcote shared worries with such an upgrade as he tried to do a the same upgrade in sewing kit https://github.com/Shopify/sewing-kit/pull/1899 So I'm not exactly sure what the foundation team decided to do with this core-js upgrade

[alexandcote]

I'm planning to do the full core-js bump during the next hack day so after BFCM most of the project will be able to use core-js 3 and new ES features.