Initial Test Case creation for System.Xml (dotnet/corefx#31129)
* Initial Test Case creation for System.Xml
* PR review comments resolution
* PR Review comments resolution
* PR comment resolution. Build files deleted
* Removed dependency on Properties and Targets file
* Added helper class to extract out XmlNodeReader construction
* Changes incorporating code review comments
* Changes for code review comments
Commit migrated from https://github.com/dotnet/corefx/commit/
ef760ce9359200f8179c2888ace0b1ff7ec44ed3