Add .NET Core 3.0 nuget e2e pipeline tests (#4695)
* bump cswinrt version
* add cswinrt
* test dotnetcore 3.0
* rename buildpacakge source
* set folder path to the package source and not the version
* refactor .netframework tests
* build .net core anycpu
Co-authored-by: Sheil Kumar <sheilk@microsoft.com>
