BluetoothRemoteGATTCharacteristic：value 属性
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
BluetoothRemoteGATTCharacteristic.value 只读属性返回当前缓存的特性值。当通过通知或指示读取或更新特性值时，该值会得到更新。