Emit type forwarders into reflection metadata

[MichalStrehovsky]

Need to come up with a mechanism to emit type forwarders into reflection metadata (so that you e.g. can Type.GetType("System.Object, System.Runtime") in addition to Type.GetType("System.Object, System.Private.CoreLib").

On Project N, we emit all the forwarders for all types we generate metadata for. We also look for forwarders in all assemblies we load. On CoreRT, there's this distinction between reference assemblies and input assemblies. It's not clear yet how do we approach this.