Update Proj-Info to use FCS and FSharp.Core from 9.0.100

[TheAngryByrd]

Fixes #218 #214
Supplants #211

[baronfel]

I think the projectsystem project is missing versioning - will take a look

[baronfel]

Alright - the asset handling for the MSBuild packages is all set now. I also saw that one package wasn't getting a version - that was due to missing packagerefs on the build-time packages. I pushed those into Dir.build.props so that everything got them at the same time and in the same way.

I also added small READMEs to the packages so that the NuGet warnings were satisfied and users might have a slightly-better getting started experience.

After this I diff'd the local packages to the latest packages on NuGet.org and the content is structurally the same - with the exception that the Microsoft.Build packages no longer pollute callers. Now they will need to add their own MS.Build compile-time references, but the README for the Ionide.ProjInfo package includes those instructions.