[docs] Update publishing section babel recommendation

[augustjk]

Reported by user here lit/lit#4416

https://lit.dev/docs/tools/publishing/#compiling-with-babel

This page still mentions the deprecated @babel/plugin-proposal-class-properties. We should update that and perhaps add links to the decorator section for details.

In the context of that page which is to publish modern JavaScript, it seems more relevant to include @babel/preset-env.