Merge: json::serialization: intro `attributes_path` as support to `class_name_heuristic`

Intro a list of the attribute names to the currently deserialized object which can be used to infer the Nit type of a JSON object to deserialize. It is not the most reliable information, some objects won't have an associated attribute like the root deserialized object and collection items.

Should help for #2246.

As a bonus, this PR improves the doc to `Deserializer` mainly to mention `errors` from `deserialize`.

Pull-Request: #2252
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>