JIT Compiler for MSBuild

Evaluation time is a non-trivial portion of small-to-medium builds and a large proportion of Visual Studio project-load time. Much of that time is spent interpreting MSBuild imports that are common, like `Microsoft.Common.props`, the .NET SDK, and `Microsoft.Common.CurrentVersion.props`.

If we could interpret these to a cacheable (in memory or on disk) form that's faster to walk through, we could potentially dramatically reduce evaluation time.

(I've been telling people I want to do this for years and years but I don't appear to have ever filed an issue for it.)