Auto add project reference based on path

[Kethku]

This tool seems like its perfect for exploratory testing of projects or doing quick experiments to test out an in development feature.

To smooth over that use case, I think it would be valuable to automatically (or with a magic command) add a project reference to whatever project is in the current path. An initial version of this could be to just do a quick check on startup if there is a csproj file in the current directory and just reference it.

Some possible issues:

• Maybe the project would have to be built first? I don't know how this system handles referencing csproj files.
• The .net version likely has to match up. This could be fixed by just trying and silently failing (or with a quick message explaining the problem)

[jonsequitur]

This capability is something we're looking at enabling for .NET Interactive generally (including for notebooks): dotnet/interactive#890.

If the scenarios you have in mind aren't captured there, please add your thoughts.