orleans: Failsafe Exception Serialization

We currently rely on all serialized types to be present during deserialization. This means that the assembly for any type transferred over the wire must be present on the receiving end. This is fine for most cases, but can be tricky for ‘unexpected’ types, such as exceptions.

Users would like to be able to see basic information about which exceptions are being thrown and from where, even if they are unable to deserialize the concrete exception. We can accomplish this using the ILBasedSerializer, adopting a special scheme for serializing Exceptions whereby base class fields are serialized first, like so: <FullTypeName><Length><ExceptionBaseClassFields><RemainingFields>

Using this scheme, we can fall back to deserializing into Exception or an OrleansFallbackException class and retain the original Message and StackTrace properties along with the name of the original exception type.

I’ve prototyped this and added a test case. I can make it PR ready.

Thoughts? Should I pursue this?