✨ build typescript types

[dudeofawesome]

This is a WIP PR to generate Typescript types from the source files, as suggested here.

However, as is, these types would not be useful as they would not be distributed with the JS via the CDN.

There are a few possible solutions to work around this:

• Update the CDN to support the X-TypeScript-Types header from Deno, as I described here. This does have the downside of not being native to Typescript though (and requiring an extra editor extension because of that).
• Add the generated types to the @types/k6 package, under a declare module. This would require altering the generated types from this PR to enable embedding like that.

[CLAassistant]

All committers have signed the CLA.