GenAPI should preserve TypeForwardedTo attributes on ref assemblies

[JunTaoLuo]

As per email discussion, we should add an option/feature in GenAPI to ensure that if a TypeForwardedTo attribute is present on the src assembly, it should also be generated in the ref assemblies by GenAPI. However, due to ambiguity in implementation, we should be able to toggle this feature on or off. The ambiguity comes from whether you want a) type-forward or the b) type in the reference assembly.

@safern @ericstj