Add object-based serialization and deserialization of polimorphic types in JSON on JS platform

[shanshin]

• implement JSON serialization (deserialization) of polymorphic type from (to) dynamic with discriminator
• add tests on object-based and array-based polimorphism encoding and decoding on JS
• fix array-based encodind polymorphism to dynamic type on JS

[ankushg]

I know this has already been merged, but does serializing to/from dynamic actually have to be part of the json format? Or should it perhaps be separate?

Asking mainly because I have a project that only needs dynamic handling, and it might be overkill to pull in all the machinery behind "real" JSON support

[sandwwraith]

@ankushg Well, since JSON is a JavaScript Object Notation, javascript's dynamic objects can be mapped on it really well. It allows us to provide first-class support for features like object-based polymorphism and interopability with JsonElement, so it's an important part.

[ankushg]

@sandwwraith definitely! My question was really if it was possible to put this in core instead of json, since dynamic is really just part of the JS language itself (as opposed to parsing JSON-formatted Strings or JsonElements, which are more external).

Right now you have to pull in the machinery that handles everything related to JsonElements just to get support for the built-in dynamic type.