Most of the logic related to type and kind retrieval belongs in the
codec, not in the various classes. Make it explicit that the codec
should handle these details.

Factory now returns a universal Decoder and a JSONEncoder to assist code
in kubectl that needs to specifically deal with JSON serialization
(apply, merge, patch, edit, jsonpath). Add comments to indicate the
serialization is explicit in those places. These methods decode to
internal and encode to the preferred API version as previous, although
in the future they may be changed.

React to removing Codec from version interfaces and RESTMapping by
passing it in to all the places that it is needed.