Add Support for Polymorphism

[Danielku15]

OData supports polymorphism via "@odata.type" annotations in objects. OpenApiQuery should support this too. Currently it is problematic as the deserializer cannot parse the JSON bind properties until @odata.type is known. But as JSON object keys are not ordered in any way, we cannot require @odata.type to be the first property.

This basically means we need to parse first the whole JSON text into a JSON DOM, and then convert the DOM into objects. This will likely degrade the performance and requires a change of the full deserializer system.