Sandbox: The KHR_texture_transform property of GLTFExport cannot be exported

@alexchuber instead of moving this thread off topic I decided to just post a new topic on how to create a custom extension handeler on export. Unfortunately I dont seem to have access to the GLTFExport api to register/unregister my own extensions on export. see: How to register/unregister custom extensions when using GLTF2Exporter