Use 9A19103F-16F7-4668-BE54-9A1E7A4F7556 for SDK-style projects

[KirillOsenkov]

Currently Xamarin.MSBuild.Sdk GenerateSolution is using the old project system Guid for C#:

mirepoix/src/Xamarin.MSBuild.Sdk/Solution/SolutionNode.cs

Line 16 in 1e6078c

static readonly Guid csprojTypeGuid = new Guid ("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}");

When generating .sln for SDK-Style projects it should be using 9A19103F-16F7-4668-BE54-9A1E7A4F7556 instead.

[abock]

This is wildly contentious and is a conflict that exists today between VS Mac (and .NET Core's dotnet sln add ...) and VS Win. I believe introducing the new 9A19103F GUID was a mistake and VS Win really needs to switch back.

See dotnet/project-system#1821 (and my take in dotnet/project-system#1821 (comment)).

[KirillOsenkov]

Seeing how this is still not solved in VSWin world, and we're still suffering because of this, the best solution is for the generator to support both so we can choose. Right now I'm just fighting the tooling.