Integration with .NET Project System #112

Microsoft has kept the .NET Project System open source since they released the first version of .NET Core. It depends on the closed source Visual Studio Common Project System (CPS), so the main purpose of that repo, I think, is to provide references for VS extension authors.

But with enough effort spent, I got a few shims that emulate the features of CPS so that the entire .NET Project System can run well to empower custom IDEs like UnoDevelop and OpenDevelop.

So, if SharpIDE integrates with this project system it can easily reach feature parity with Visual Studio 2022/2026.