Bug: Exclude inaccessible interface methods from codegen about orleans

[ReubenBond]

What would you like to see happen here? Internal interfaces are acceptable. Protected members within them could possibly be supported with a codegen change to mark the corresponding member on the generated proxy as protected also

[alrz]

What would you like to see happen here?

The implementation must be public or explicit, but it's simply throwing an unreachable exception because the code from ISomeGrain client won't get there anyways.

Note this member is not callable from "outside" but at that point we're already on the server, not client.

[alrz]

simply throwing an unreachable exception

Correction: that wouldn't be correct for internal methods though