Replace TBD XML doc placeholders in Akka.Serialization

[MattKotsenas]

Changes

Replace TBD XML doc placeholders in the Akka.Serialization namespace with useful documentation. Two files updated:

• Serialization.cs - documented WithTransport<T> (transport context setup for actor ref serialization), AddSerializationMap (type-to-serializer mapping), Deserialize overloads (bytes/serializerId/type and bytes/serializerId/manifest), and FindSerializerForType
• NewtonSoftJsonSerializer.cs - documented Settings and Serializer properties, and the SurrogateConverter class and constructor

Partial fix for #3435.

Checklist

• This change follows the Akka.NET API Compatibility Guidelines.
• I have reviewed my own pull request.
• Changes in public API reviewed, if any.

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).