NuGet Support in Visual Studio for Mac 17.4

Changes

NuGet 6.3.1 support
Fixed multiple NuGet.Config load error dialogs
Fixed wrong NuGet.Config file path when failing to save file

More information on all the new features and changes in Visual Studio for Mac 17.4 can be found in the release notes.

NuGet 6.3.1 support

NuGet 6.3.1.1 is now included with Visual Studio for Mac 17.4.

Fixed multiple NuGet.Config load error dialogs

On opening or creating a new solution, and the global NuGet.Config file was invalid, two error dialogs would be displayed indicating a problem with the NuGet.Config file.

Now the error dialog is only displayed once when opening a solution.

Fixed wrong NuGet.Config file path when failing to save file

When there is an error saving the NuGet.Config the error message shows the path to the file. However this was using SpecialFolder.ApplicationData instead of the correct path ~/.nuget/NuGet/NuGet.config.