_createCodec
Subclasses must return a runtime content codec describing how to turn a downloaded tile payload into a Cesium3DTileContent. See Cesium3DTileset._runtimeContentCodec for the expected shape.
Subclasses must return a runtime content codec describing how to turn a downloaded tile payload into a Cesium3DTileContent. See Cesium3DTileset._runtimeContentCodec for the expected shape.