can not use dot notation in variable steps/flows

[Francois Falala-Sechet]

Describe the bug
goto $something.name does not work, which is inconvenient in situations like this:

To Reproduce

start:
  say Question(
    "Where do you want to go next?",
    buttons=[
      Button("A", stepname="stepA") as btnA,
      Button("B", stepname="stepB") as btnB,
    ]
  )
  hold
  do clicked = event.match(btnA, btnB)
  if (clicked) goto $clicked.stepname

  say "Please use one of the buttons!"
  goto start

stepA:
  say "I'm in step A!"
  goto start

stepB:
  say "I'm in step B!"
  goto start