ensure esm, cjs, typescript builds are usable

[michaelglass]

I built a test repo with some test commands that should verify if we're packaging nlx libs correctly.

I don't think we are.

Some issues:

• package.json expects the main field to be a commonjs lib (fixed in #119)

• (not a umd / web problem) node checks either the file extension (.mjs -> esm, .cjs -> commonjs) or the type: field in package.json to figure out whether the dependency should use common js or esm packaging. I thought this blog post was helpful
  Some solutions:

  1. we rename the two files .mjs / .cjs
     - pros: it works without a type field in package.json
     - cons: apparently it's not supported by all build tools

  2. we build two different package.jsons for js and esm
     - pros: it should work for all builds tools
     - cons: it's a bit more complicated

• mixing default & named exports isn't properly supported by commonjs (or by our umd build)

let's resolve the second and third issue and

• add the test-repo build scripts to CI
• automate the browser packaging test and add it to CI as well (puppeteer?)

[michaelglass]

@jakub-nlx asks in slack, "Do we need to support cjs?"

[peterszerzo]

@jakub-nlx @michaelglass we have one user left on a legacy webpack build system, we expect them to be off within the next few months. After that, I would say that we should 'support cjs in a scrappy way', as in I would be comfortable telling users that if they really want cjs, they need to change the import path to @nlxai/chat-core/lib/index.cjs if they want to get to the compatible file.

[michaelglass]

Ok then I propose a third option:

1. we rename the common js file to .cjs
2. we add a type:module to all the package.json files

let's see if that makes the test repo happy.