Implement proper interop to PInvoke for structs contataining an object ref

[LLITCHEV]

Currently on Windows the CLR uses a VARIANT type to pass the object ref to the native PInvoke.
For non Windows systems it throws a TypeInitializationException.

After discussing with interop team a work is underway to either throw UnsupportedException or to properly marshal the obj ref.

[AaronRobinsonMSFT]

@jkoritzinsky We throw NotSupportedException right? I think this issue can finally be closed.

[jkoritzinsky]

I believe we throw a MarshalDirectiveException, but I need to check.

[jkotas]

We throw System.Runtime.InteropServices.MarshalDirectiveException: Cannot marshal 'parameter #1': Invalid managed/unmanaged type combination (Marshaling to and from COM VARIANTs isn't supported).. I do not see anything to fix here.