Type helper for low-level cdp request

[ysmood]

We don't need full type support, a better way to do it is to add optional type helper to help us type the json objects that chrome uses.

By this optional way, the user can still interact with the latest chrome API even if the type helper is outdated.

The schema to use is on this page: GET /json/protocol/

The way https://github.com/mafredri/cdp or https://github.com/chromedp/chromedp did it is not good enough. Their implementations are tightly coupled with their high-level lib. Therefore their type is hard to be used as a standalone lib when someone only wants to use the type to generate a request JSON payload.