Recursively select Assembly references for the AssemblyGenerator

[jeremydmiller]

Exact same issue we hit w/ Marten when we were using the Roslyn codegen.

When we do the dynamic compilation, you need to explicitly tell Roslyn about every single assembly that needs to be referenced and used by the code being generated. That includes any assemblies that the application references. I think we need to either:

1. Use the DependencyContext to just add every loaded assembly. Not sure if that would hurt anything, and it might be easier mechanically
2. When adding an assembly to AssemblyGenerator, have it quietly walk up the dependency tree of that assembly and add its dependencies.