Module System to support Browser and NodeJS runtimes

[rido-min]

We started the Agents-for-js following botbuilder-js, and one of the decisions made at the beginning of the project was to target commonJS module system, as this has been the most compatible format.

Now that we are adding Browser support in #398 , I'd like to discuss if we could target ES6 so we can allow importing directly from a CDN - such as unpkg or jsdelivr - with importmaps, without having to produce a bundle with tools like webpack or esbuild.

The downside is that we will force everyone on ES6 imports, and require style wont be supported.

To keep compatibility, we can also produce packages targeting CJS and ESM like zod does.

@ceciliaavila @sw-joelmut thoughts?

/c @MattB-msft

[sw-joelmut]

I think it will be a good change to only support CJS and ESM and avoid esbuild to have the IIFE browser (window.Agents assignment) compiled file for example.
With CJS we will support Node (use of require) and with ESM all things that understand modules (use of import), and for the looks of it, the zod package only uses Typescript to compile both, which is great to avoid build tools, but in the case of Copilot Client, when importing a library e.g. axios, we need to add it to the importmap in the sample since we are not including the dependencies into the built code unless we use a bundler like esbuild

It will be helpful if we can define the importmaps in the library, so the customer doesn't have to, but I think it isn't possible right now, unless I'm missing something.

Here is an example of using importmaps with modules