Fires an event with the current value of the ready state of control.
The ready state can be one of the following values:
Default initialization state
Control is currently loading its properties
Control has been initialized
Control has enough data to be interactive but not all asynchronous data is yet loaded
Control has all its data
Use GetReadyState to determine the control's current readiness.
InternalSetReadyState changes the ready state to the value supplied, then calls FireReadyStateChange.