Investigate if Gson adapters could be generated easily about kotshi

[JakeWharton]

I'm against this as I'd like to see Gson whither away in a slow death. It's blown its complexity and API budget for continued tolerance and historical baggage makes change nearly impossible.

However, this should be trivial as the Moshi APIs currently used by this project were modeled from the best parts of Gson.

I would think it'd go something like this:

• Rename @JsonSerializable to something library-specific (prefix with Moshi or @MoshiJsonAdapter or @GenerateJsonAdapter or whatever).
• Renamed @KotshiJsonAdapterFactory in a similar fashion.
• Introduce Gson variants of those two annotations.
• Refactor the processing steps to use an enum which contains various information like:
  • A ClassName for the adapter and factory.
  • A ClassName for the JsonReader and JsonWriter.
  • Strings for the various method names.

The generated logic is 99% shared and the enum provides the differently named bits depending on which annotation is present.

[ansman]

I agree, I don't think it should be done too. I haven't had any requests for it so I think it could probably be skipped.