[ds] allow a component to implement ServiceFactory / PrototypeServiceFactory

[laeubi]

Currently a component must implement the services it exposes through the service factory.

There are sometimes cases where one want to expose a service with DS, but creation of such service won't be possible by DS what for example includes:

1. The service is not an interface but a final class that needs constructor arguments that are dependencies or need to be constructed from injected services, java records are a good example as well as many (non OSGi) libraries
2. The constructor is invisible and instances can only be created by a static factory

Current state

This currently forces one to use some indirection, e.g have a component that does not expose a service, injects a bundle context and then register/unregistered the service. This contradicts the idea of letting the SCR manage the service lifecycle, for example this means such a component must always be active and possibly registering services that are never used.

Proposed solution

If a component exposes exactly one service S instead of requiring the component to implement this service it is allowed to alternatively implement the ServiceFactory / PrototypeServiceFactory interface with the generic parameter of <S>.