- T value
A callback used to start the listening of an object and return a function that cancels the subscription.
It is called the first time the value is obtained (through InheritedContext.value). And the returned callback will be called when InheritedProvider is unmounted or when the it is rebuilt with a new value.
typedef StartListening<T> = VoidCallback Function( InheritedContext<T> element, T value);