Allow coder factories to create Coders for a wider range of types

By allowing the CoderFactory to see they type it can look at annotations on the type allowing:

• @DefaultCoder to become a CoderFactory
• Creating a ProtoCoderFactory which delegates to the ProtoCoder for all Message types
• Creating a SerializableCoderFactory which delegates to the SerializableCoder for all Serializable types
• Creating a WritableCoderFactory which delegates to the Hadoop WritableCoder for all Hadoop Writable types

This requires plumbing through TypeDescriptor as the primary method of looking up coders within the CoderRegistry

This also removes the concept of fallback coder providers since every coder factory is treated as a fallback.