[REVIEW ONLY] Split View Refactoring

This is the refactoring effort to move Working Set API's and start deprecating some of the DocumentManager APIs

This probably isn't ready for prime time consumption but want to get any feedback on the approach and if there is anything I forgot. 

Also I encourage as much test exposure as possible to make sure nothing is broken.
Because `DocumentManger.removeLIstFromWorkingSet()` is deprecated and the replacement does not support the `clearCurrentDocument` discreet -- it was already an exported API but private so I just removed the private part and call it from here to close the document.  This will get refactored again.