[repository] provide a RepositoryReference interface to find out the repository of a Resource

[laeubi]

If a Resource originates from a Repository it is sometimes useful to find other Resource from that.

Adding a RepositoryReference interface a resource can optionally implement would allow to discover the originating repository.

[timothyjward]

Why would we need a new interface? We could add this method to RepositoryContent, which already exists to mark a resource as having come from a repository.

[laeubi]

I have seen RepositoryContent more as a way to access the stream of bytes and even if the javadoc says that all Resource from a repository must implement this I can see cases where a Resource exits in a repository but has no "real" content, but if it is easier RepositoryContent can be enhanced of course.

One thing that came into my mind was that e.g. Bundle and similar has an adapt(...) method, maybe one should have such one for Resource as well, then it could be provided by adaption pattern to get access to the repository (and maybe other objects as well) without new interface. This would even allow more flexibility in discover internal representations as well.