[MSBuild] Use MSBuild assemblies from NuGet instead of Mono's installation

We had to revert https://github.com/xamarin/xamarin-macios/pull/21471 on https://github.com/xamarin/xamarin-macios/pull/21670 in order to fix https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2304182 we need to investigate a better fix than reverting.

cc/ @emaf @mauroa @rolfbjarne 