finalState method
Adds to the state tree a description of a final state, identified by stateKey. The behavior
of the state is configured by the build callback.
A final state is a terminal state for a state tree. Once a final state has been entered, no further messsage processing or state transitions will occur.
A final state never has any child states, and is always a child of the root state.
Implementation
void finalState(StateKey stateKey, void Function(FinalStateBuilder builder) build) {
var builder = _StateBuilder._(stateKey, null, null, true);
build(builder);
_addState(builder);
}