Drop CommonJS support in Node packages, use "type": "module"

[nolanlawson]

There is at least one dependency in our Node packages (e.g. estree-walker, which is a dependency of @lwc/template-compiler), which we cannot currently update because it dropped support for CommonJS.

Unfortunately ESM is kind of viral – if you want to import ESM synchronously, you basically need to use "type": "module" yourself. So updating our packages to "type": "module" would be a breaking change for our consumers.

[git2gus]

This issue has been linked to a new work item: W-12114588

[nolanlawson]

In practice this would probably mean converting our entire repo to "type": "module". Not a bad idea, but definitely a breaking change.