The go runtime was not tracking aliases in a way that enabled it to
return an alternate proxy to an object instance when that had previously
been returned as a different, singular interface.

This change keeps tack of the "first ever" registered instance against a
given InstanceID (as this is likely the one that was natively
constructed), but also to all proxy aliases to the same InstanceID, so
that it can later return an existing proxy that can be converted to a
desired type.

Fixes #2688