This commit adds conditional support for propagating the
`ReadModelOptions` variable to the root JsonValue class for all of
its children. CesiumGltfReader was designed with the philosophy that
extensions should be well defined and that CesiumGltfReader should
take responsbility for decoding extensions. This is a fine idea, but we've
ran into a usecase where we need CesiumGltfReader to support decoding
new / developing / unknown / WIP extensions.
This commit adds the `deserializeExtensionsAsJsonValue` bool to ReadModelOptions
and for each ***JsonHandler, forwards it to the root via super() constructor invocations.
This opens the door for other "while serializing" options to be stored in
ReadModelOptions
The deserializeExtensionsAsJsonValue variable itself instructs CesiumGltfReader
to add any extensions it encounters in the Gltf string as a `JsonValue::Object` inside
the std::vector<std::any>, so that users of the libraries can retrieve it and do their
own casting.
Kevin Ring
Samuel Vargas
Marco Hutter