File rooting bugfixes + VS 19 json fixes

[edkazcarlson-ms]

This PR addresses 2 main bugfixes:

1. The extension does not play well in VS 19 after I tried to upgrade the ver of the json nuget. Here is a blogpost about it but in short every ver of VS ships with its own ver of the newtonsoft json nuget, but when you use a ver that is outside the one that it is shipped with, it can cause issues. In this case, vs 19 comes w/ newtonsoft 12 and so it didn't like how I increased the ver to 13.
2. When opening files through the drag and drop or through the File > Open > File and you don't have the appropriate folder/solution open, it will fail to link the relative file path in the sarif object to the absolute file path on disk if they file seperators are different (/ vs )

[EasyRhinoMSFT]

Shoot, I forgot to block on the Newtonsoft thing, sorry. #Resolved

[EasyRhinoMSFT]