+str #16077 implement Zip and friends for javadsl

This PR will contain more commits - for now it's just the Zip operation but wanted to show/get-early feedback on the method I used to not duplicate the implementation while being able to emit java Pairs or Tuple2s.  

Refs #16077
Yeah, agreed - do you think we should tackle that one now (as in, try to lift this PR into the DSL level (had trouble with that)). If so let's stash this PR and I can hit it again on monday. Or if it's OK for now please merge :-)