[sensor] Not readonly properties for state and readvalue

[cuiyanx]

State and readvalue of sensor should be readonly properties, but actually it can be modified.

W3C Sensor APIs:

readonly attribute SensorState state;
readonly attribute SensorReading? reading;

code for test state:

middleState = sensor.state;
sensor.state = middleState + "love";
assert(sensor.state === middleState, "sensor: state is readonly property");

code for test reading(AmbientLight):

middleNum = event.reading.illuminance;
event.reading.illuminance = middleNum + 1;
assert(event.reading.illuminance === middleNum, "sensor: reading is readonly property");

[cuiyanx]

fixed and closed