Use custom stream writer for Xml output formatters

[kichalla]

Follow up to #2496

Currently Xml output formatters (DCS and XmlSerializer) do not use the custom stream writer.

XmlWriter however provides an overload which takes in a text writer. We should be able to provide the custom stream writer that we built as part of #2496

[rynowak]

This should probably be generalized to 'do a find and replace for non-disposable stream'. There's a bunch of functional tests where the old pattern was used, and we want as much as is feasible our tests to reflect our recommendation for a user writing the code.