Support deserialization of generic types that are JsonSerializable.

[srnagar]

          This looks good to handle `List<JsonSerializableType>` but nothing more than that. This is good to get us unblocked but we might want to look into more generalized handling in the future for stuff like `Map<String, JsonSerializableType>` or `List<List<Type>>`.

Originally posted by @alzimmermsft in #44208 (comment)

[joshfree]

@srnagar could you make this issue title more concise?