Refine JSDoc / TypeScript types for plugins

[dobesv]

Starting working on improving the JSDoc / TypeScript a bit so that I could better understand the types here.

I'm not totally sure these are quite correct.

Also - can plugins define all the events defined in events.js ? It seems like the JSDoc currently only lists a few events.

[dobesv]

Working on this it does feel like maintaining separate .d.ts files would actually be easier than trying to figure out JSDoc magic I need to do in order to produce good TypeScript definitions.

[rene-airtame]

This would be a very welcome addition as all the plugin methods are typed simply (...params: any[]) => any now.