projections.g.cpp excludes the C++/WinRT header if no interfaces from it are included in the projection but specialized generic types and etc. still are. #154

If you include only runtime classes from a namespace using a filter, it would in include their static interfaces and constructors in the projection of the runtimeclass but none of the instance interfaces. It appears that in this scenario because there are none of the latter, it will include the RN/WinRT <namespace>.g.h but not the corresponding winrt/<namespace>.h header. For example, this causes a build break supposing any of those runtime classes is referenced in projections.g.cpp for specializing a generic interface (e.g. IIterable).