Changes to enable XML Output Formatters.

Functional tests for Output Formatters are not a part of this PR. Will follow up with Functional Tests after @harshgMSFT's conneg check-in.
You are talking about the CloseOutput option in WriterSettings? Is there something we can do about this? Do you think we should manually do `WriterSettings.CloseOuput = false` before creating XmlSerializer/DataContractSerializer object?