See Microsoft/msbuild#1661

The RoslynPackage type originally lived in a seperate assembly than
Microsoft.VisualStudio.LanguageServices when it was important for us
to be able to support the core parts of Roslyn being installed atop
the existing Visual Studio 2013 language services. This is no longer
a supported scenario anywhere, so we should just get rid of the
assembly.

Doing this is easy, it's just a matter of moving the files and related
assets to the LanguageServices assembly. A MEF interface is added
to prevent a circularity around triggering a load of stuff in the
SolutionExplorerShim. That could be delt with later by moving the core
of that code back to LanguageServices, but I don't want to touch that
now since it's very sensitive.

This change moves the contents of VisualStudioSetup into the open,
merging with (and consuming) VisualStudioComponents. The Components/
Setup split originally existed as a way to allow multiple Roslyn-using
components to have a single source of truth of the MEF exports. This
meant you could have either the interactive window, language services,
or both installed and everything worked. This was important when we
were atop Visual Studio 2013, but now that we're integrated it's buying
us nothing.

The VSIX ID from VisualStudioComponents is preserved so that way any
extensions that declared a dependency on it will still work.

Previously the command line tests were looking in various directories for csc.exe/vbc.exe. Instead, add a reference to csc/vbc project to the command line unit test assembly, so that we always test what we build and not depend on directories outside of Roslyn.
To make it easy to test the default .rsp file this change links it into the command line unit test project and includes it to resources. The tests then extract the .rsp from the resources and save it to a temp file for testing.
 (changeset 1285693)

Splits Microsoft.CodeAnalysis, Microsoft.CodeAnalysis.CSharp and Microsoft.CodeAnalysis.VisualBasic into portable and desktop assemblies.

Existing Core\Source, CSharp\Source and VisualBasic\Source directories are renamed to Core\Portable, CSharp\Portable and VisualBasic\Portable.
New sibling Desktop folders are added and non-portable source is moved there.
"System.Runtime" references has to be removed in order for the portable project system magic to automatically add facade references.
 (changeset 1281686)