Fix Windows Inbox build failing on 1) building raw api tests and 2) referencing _winml namespace in onnxruntime.dll (#3872)
* add build inbox flag
* remove raw tests and wstring for utf filenames
* enable raw tests
* use ToWideString
* create new utf8 helper
* update string helper to utf8
Co-authored-by: Sheil Kumar <sheilk@microsoft.com>