Reference loop when using fsm.Next()

[matt2e]

Problem:

• Prereq: feat: allow FSMs to specify the next event to send #1723
• Having a fsm declared causes go to fail to build because the variable references funcs that reference the variable.

Not sure the best way to get around this, while also being obvious from a dx point of view.

Here's some options:

Option 1: Wrap it in a function:

func fsm() *ftl.FSMHandle {
	//ftl:retry 2 1s
	var fsm = ftl.FSM("fsm",
		ftl.Start(StateA),
		ftl.Transition(StateA, StateB),
        ...
	)
	return fsm
}

Positives:

• works out of the box without schema extraction changes

Negatives:

• hard to remember to use var rather than := (:= does not support having attached Docs out of the box)
  non obvious whether retry directive goes on function or variable (no warning/error if they get it wrong)

Option 2: Allow separate var declaration and assignment

//ftl:retry 2 1s
var fsm *ftl.FSMHandle

func init() {
	fsm = ftl.FSM("fsm",
		ftl.Start(StateA),
		ftl.Transition(StateA, StateB),
        ...
    )
}

Negatives:

• retry directive is now separated from the rest of the definition of the FSM

[matt2e]

Going with this:
ftl.FSMNext(ctx, event)