Regarding the value that MLDevicePreference and MLPowerPreference can take, WebNN uses "default" as one value (https://webmachinelearning.github.io/webnn/#api-ml) but I feel maybe "auto" is more suitable because in this case, the backend will automatically determine the running environment. "auto" carries more message than "default". What do you think?