chore: provide CJS and ESM bundle

[JoviDeCroock]

This PR allows us to follow the mainstream way of publishing a library, giving us the ability to provide a tree-shakeable esm bundle, a cjs bundle for main and an umd bundle for browser.

As mentioned in: #229
And as done in other repositories from apollo:

• chore: provide esm bundle react-apollo#2677
• Typescript incremental builds using project references, test type checking, better dev workflow apollo-client#4261

I also think it's quite safe to say that it would be appropriate to upgrade the rollup and babel deps, if this is desired I feel up to the task. Just reply it here

[benjamn]

I think there's a more fundamental issue that should precede this work (though I fully support standardizing our publishing formats): this library is still just CommonJS rather than TypeScript or even ESM. Not asking you to do that conversion yourself, but I think it's time someone did it!

[JoviDeCroock]

Allright, I feel up for that. So you would like to see this repository converted to TypeScript. I'll probably have some time to do that this sunday. :D thanks for looking at this already. I'l lleave this open while I do the conversion or?

Are the flow types obsolete then or? Don't have any flow experience

[JoviDeCroock]

To be honest, I've been giving it a try but converting this repository to TypeScript is non-trivial. A lot of types that should be a 1-1 mapping from graphql/language are a bit misused it feels like... Could be just me misunderstanding some parts