💻 Roles of variables: add stepper in for loop

[juliabolt]

I've added the stepper role, it works with for loops, but other kinds of steppers are not working yet.

How to test

Follow these steps to verify this PR works as intended:

• change the feature flag showRoles in debugging.ts to true
• go to Hedy level 11 and run this program (or something similar) in the debugger:

  for counter in range 1 to 10
  print counter
  print 'Ready or not. Here I come!'

• check that in the variables view, the role that is shown for the variable counter is stepper.

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• [ x] Contains one of the PR categories in the name
• [ x] Describes changes in the format above
• [ ] Links to an existing issue or discussion
• [ x] Has a "How to test" section

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[juliabolt]

oops let me rebase this branch first