Auto start layout engine when hydrating server rendered content

[joeldenning]

It should not be possible to have a different layout definition in the browser than the one that was server rendered. Easiest way to solve this is to add all information to window.singleSpaLayoutData and use that information to automatically construct a client-side layout engine. Maybe something like this:

// client-side code
import { hydrate } from 'single-spa-layout';

hydrate()