Add support for specifying other default values for return values
Add support for specifying other default values for return values

This allows us the override the base.SomeVMethod return values in case
the native type doesn't implement the VM.

GStreamer/gstreamer-sharp,freedesktop-unofficial-mirror/gstreamer__gstreamer-sharp,freedesktop-unofficial-mirror/gstreamer__gstreamer-sharp,gstreamer-sharp/gstreamer-sharp,GStreamer/gstreamer-sharp,Forage/gstreamer-sharp,gstreamer-sharp/gstreamer-sharp,gstreamer-sharp/gstreamer-sharp,GStreamer/gstreamer-sharp,Forage/gstreamer-sharp,Forage/gstreamer-sharp,Forage/gstreamer-sharp,freedesktop-unofficial-mirror/gstreamer__gstreamer-sharp