Verify compatibility with node.js ESM implementation

[Morgul]

Newer versions of node now support ESM module, however the workarounds we've been using for years are much more lax than this implementation. We need to make some changes to adjust.

• Add "type": "module" to package.json
• Convert all local imports to have the .js extention
• Other issues as they come up

(Note: this is not an exhaustive list!)

[PieceMaker]

Thanks! We'll get on it in the near future.