The recommendation tests can be run in parallel but were in an assembly which
had many other tests that could not. Splitting out into a separate assembly
which is designed for parallel runs.

This change makes foreground scheduling code predictable in the IDE
tests.  Instead of using a static to hold the data we use instance
values.  The static data the instance values are populated from are not
100% predictable but far more so than they used to be.

* This updates all references to nuget.exe to use the copy in the root.
* This deletes all NuGet.config and NuGet.exe files that are not in the root.
* This removes all references to NuGet.targets (which is obsolete and no longer exists)

Rogjt mpw we build a boostrap version of csc and vbc and bootstrap
with those running on Mono. This commit switches us to build a CoreCLR
compatible csc and then running the boostrap on CoreCLR

Right now the full set of Linux CoreCLR runtime assemblies is not
available on NuGet, so we substitute with some assemblies we stash in
our NuGet ZIP package.

Diagnostics.csproj was under Roslyn/Diagnostics in solution, but everything there is removed and the only project referencing Diagnostics.csproj now is src/VisualStudio/VisualStudioDiagnosticsToolWindow/VisualStudioDiagnosticsWindow.csproj, so move Diagnostics.csproj under Roslyn/VisualStudio and remove Roslyn/Diagnostics from solution.

All the projects depend on this project are already moved to dotnet/roslyn-analyzers repo.

Everything under dotnet/roslyn/src/Diagnostics/FxCop is moved to dotnet/roslyn-analyzers/src/AnalyzerPowerPack .

Everything under dotnet/roslyn/src/Diagnostics/FxCop/Desktop.Analyzers is moved to dotnet/roslyn-analyzers/src/FxCop/Desktop.Analyzers.

Everything under dotnet/roslyn/src/Diagnostics/FxCop/System.Runtime.InteropServices.Analyzers is moved to dotnet/roslyn-analyzers/src/FxCop/System.Runtime.InteropServices.Analyzers.

Everything under dotnet/roslyn/src/Diagnostics/FxCop/System.Runtime.Analyzers is moved to dotnet/roslyn-analyzers/src/FxCop/System.Runtime.Analyzers.

Everything under dotnet/roslyn/src/Diagnostics/CodeAnalysis is moved to dotnet/roslyn-analyzers/src/CodeAnalysis.

Everything under dotnet/roslyn/src/Diagnostics/Roslyn is moved to dotnet/roslyn-analyzers/src/Roslyn.

Move TestUtilities.csproj and TestUtilities.FX45.csproj to separate directories to accomodate current nuget limitations

Update the DNX build tools, which fixes #3876. Now that the
bug is resolved, add the CoreCLR projects directly to the
compiler solutions.

Added one analyzer CA2153 into Desktop.Analyzer.
Addressed the code review comments and removed unused helper code.

This is the start of our unit test assembly for our MSBuild assets.

This change adds a couple sub folders (Features, Host, Repl, Setup) and moves BasicVisualStudioRepl back to Interactive.

It's confusing for new users to have the Roslyn solutions nested
inside the src/ directory and there's really no good reason those where
there in the first place. This moves them to the root directory, except
for the Toolset.sln solution, which is only for building Roslyn in CI
scenarios and has been moved to the build/ directory.