Context Change: #23557

This PR added a reference to System.Threading.Tasks.Extensions in the MS.CA project. This effectively makes it a dependency of anything in Roslyn as that is our root most project. Yet our tooling did not catch three places where we needed to re-state our dependency on this DLL:

1. Microsoft.CodeAnalysis.swr (fixed by Add TaskExtensions to compiler package #26703)
2. Microsoft.Net.Compilers.nuspec
3. Microsoft.NetCore.Compilers.nuspec
4. VS.Tools.Roslyn.nuspec

I'm unsure that there is really tooling that can help us with 2 or 3 above. Need to add some consistency checks to ensure that everything else is updated in the case 2 / 3 is changed.