This is a simple module but took a bit of work because:
* It wraps a Promise that can return basically anything. In a pure TS
codebase we'd solve these with generics, so you could do `new
TaskQueue<T>` where `T` will be what's returned from the queue, but
because we're calling that from JS we can't yet. I've left a TODO and
once we migrate the call sites to TS we can do a much better job than
the `void | any` type I've gone with for now.
* It was used in typedefs via `Puppeteer.TaskQueue`. I've removed that
entry from `externs.d.ts` in favour of importing it and using the type
directly. This does mean that we have imports that ESLint doesn't
realiase are actually used but I think this is better than maintaining
`externs.d.ts`.
This updates our `tsconfig.json` so it emits our JavaScript files as
well as type checking them. We compile into `./lib` which we then ship
in our npm package. The source code has moved from `./lib` into `./src`.
Because the `src/` directory is exclusively JS files, this change is a
no-op in terms of code functionality but is the first step towards being
able to replace `src/X.js` with `src/X.ts` in a way that allows us to
migrate incrementally.
The `lib` directory is gitignored, and the `src` directory is
npmignored. On `npm publish` we will now run `npm run tsc` in order to
generate the outputted code.
