[Bug] Statemachines inside parallel states don't react to global triggers

[TdXYZ]

Given the following statemachine configuration:

private StateMachine _stateMachine;

void Start()
{
    StateMachine a = new();
    a.AddState("A");
    a.AddState("B");
    a.AddTriggerTransition("T", "A", "B");
    a.AddTriggerTransition("T", "B", "A");

    StateMachine b = new();
    b.AddState("C");
    b.AddState("D");
    b.AddTriggerTransition("T", "C", "D");
    b.AddTriggerTransition("T", "D", "C");

    _stateMachine = new StateMachine();
    _stateMachine.AddState("root", new ParallelStates(a, b));
    _stateMachine.Init();
}

Using _statemachine.Trigger("T") will not cause a and b to perform their transitions. This unfortunately makes ParallelStates useless for statemachines that rely heavily on trigger transitions.

This can be fixed by having ParallelStates implement ITriggereable. There is however a potential issue that should be addressed. Say that statemachine "a" has some nested statemachines and statemachine "b" has a transition whose guard checks ActiveStateName of one of those nested machines. An Exception will be thrown if the nested machine is not the active state of its parent machine.