Consider moving reified overload of `encodeTo` and `decodeFrom*` into popular formats

Otherwise, the tooling starts crumbling and suggesting wrong overloads with lack of discoverability.

Also, things like `Json.encodeToString(foo)` and `Json.encodeToString(FooSerializer, foo)` live in different packages, providing weird autocompletion side-effects (when tab- based completion accidentally import the wrong method)