In the new SDK we no longer have a need for ProjectGuid. This change
will:

- Remove ProjectGuid from project files
- Remove Name + Project items from ProjectReference entries
- Change BuildBoss to enforce both of these items

This is an automated migration of our project files to the new SDK /
PackageReference.  It is done using the tool located here:

https://github.com/jaredpar/ConvertPackageRef

The Compilers.sln solution is compiling again and tests which don't
require AppDomain support are running again.  There is a bit of work
that is needed for AppDomains that I want to separate out.  In
particular the separation to portable means we have to redo some of the
serialization code.

The TestUtilities project should be our portable unit test helper.  This is part one of rearranging our sources to reflect that reality.  I'm separating it out because it involves a significant code move that
will make the actual rework part harder to review.

This is the project which will hold the CoreClr capabilities for our test infrastructure.  In particular it will hold the code for using AssemblyLoadContext to manage our isolated test boundaries.