* chore: migrate src/JSHandle to TS
There's a few TODOs in here that all depend on typing the
`ExecutionContext.evaluateHandle` properly so that you can properly
declare what types you're expecting back. Once I've done that file (it's
next on my list) I will loop back and improve the types here, fixing
these TODOs.
* Fix doclint for {}
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.
