Make f-prime's testing utilities for state machines public #876
Description
Following a small discussion after #687 (comment):
F-prime uses helper utilities in FppTestProject to test state machines, but these helpers are not included in the build / are not accessible to users. It would be quite nice to document these and make them accessible to users to test state machines. This is also a bit related to nasa/fprime#4018, but nasa/fprime#4018 is a more long-term plan / solution.