adopt a bundle friendly and ESM compatible fork of escodegen

[thescientist13]

Summary

As reported upstream in estools/escodegen#455, there is a key issue in that in order to use escodegen, you need to have a process that understands how to handle a require of JSON, as can be seen in WCC's custom rollup configuration for bundling a CJS version of WCC

exports.version = require('./package.json').version;

Details

So for anyone using WCC, like Greenwood, its required to add a JSON plugin, in our case for Rollup.

Also while we're here, might as well refactor for ESM.