ExportService gets removed and instead a global class registry is added.
The `init.js` file is split into `init_sync.js` and `init_async.js`
so that synchronous code that isn't dependent on imports is guarenteed
to run before initgui.js. The globalThis scope and service-script API
now expose `def`, a function for registering class definitions, and
`use`, a function for obtaining registered classes.
In the first pass I add a `register` method and update `defineComponent`
so it calls `register` as well. This made it possible to create a
proof-of-concept for registered classes. Additionally ExportService was
added to expose registered classes to service scripts. This first pass
works, but it would be better if all types of classes (components or
otherwise) were registered via the same method.
Nariman Jelveh