[RFC] Modernize package

Problems:

1. Namespaces are considered a legacy feature and its recommended to use ES modules instead
2. Similar are Triple-Slash directives which we use to register the types
3. Our current approach does not really allow to type event-bus events or app capabilities

To register types like for eventbus or capabilities we would need to add them to @types which is not likely a viable way. I also tested using different type roots configuration which also does not work as intended.

So I think the proper way nowadays would be to export the types directly as types and let the app declare them where needed.

Meaning we could e.g. have exports like:

import type { globals, OCP, OC } from '@nextcloud/typings'
// or if for a specific version:
import type { NextcloudGlobals, OCP, OC } from '@nextcloud/typings/v20'

which you then use in an app like this:

// in 'src/globals.d.ts'
import type { NextcloudGlobals, OCP } from '@nextcloud/typings/v20'

declare global {
    interface Window extends NextcloudGlobals {
        OCP
    }
}

you could also type server events the same way:

// in 'src/eventbus.d.ts'
import type { CoreEvents } from '@nextcloud/typings/v31'

declare module '@nextcloud/event-bus' {
    export interface NextcloudEvents extends CoreEvents { }
}

Review the current namespace and triple-slash declaration structure in @nextcloud/typings, then compare it with the proposed versioned imports such as @nextcloud/typings/v20. Check the globals.d.ts and eventbus.d.ts augmentation examples; done means types can be imported directly and extended for globals and CoreEvents without the current registration approach.