Add ObjectSerializer to support serialization of known types without generics

[ReubenBond]

This adds ObjectSerializer, which has Serialize and Deserialize methods which accept a Type as a parameter. The Type parameter is the expected type of the value being serialized/deserialized.
In cases where the type exactly matches the type which was serialized, Orleans will not write full type information to the payload, and can instead set a flag in the payload indicating that the value is the expected type.
This means that the Serialize and Deserialize calls must have the same exact Type value or the deserialization may not know how to deserialize the value.

This complements the existing classes:

• Serializer, which has generic Serialize<T> and Deserialize<T> methods, where T is the expected type.
• Serializer<T>, which has Serialize and Deserialize methods which use the class' T as the expected type.