Add a simple Roslyn benchmarks

Add a simple Roslyn benchmarks

Add Benchmarks for Roslyn C# compilation and dataflow analysis.

The `managed/Compilation` test is similar and potentially now somewhat redundant. I left it alone but updated its dependencies since they need to agree with the new test.

I had to manually edit the `project.lock.json` files to remove the analyzers entries under libraries, to avoid a null pointer error in the PrereleaseResolveNuGetPackageAssets task (there's no language set for these projects so the attempt to deduce the appropriate set of analyzers fails).