Overhaul how transitions are stored in FlightPlan XML, and how
they’re exposed to Nasal. Simplify the Nasal access by making
‘sid_trans’ and ‘star_trans’ writeable.
Extend the unit-tests a lot to cover this, both from C++ and also
from Nasal
As part of this, overhaul the ownership of FlightPlan delegate
factories, to make it safer (use ref-counting of the factories,
and allow the factory to customise delegate clean-up behaviour)
One test so far, attempting to reproduce a bug I see with the 737.
Note these tests are skipped unless you have procedures available
and set a magic env var to find them.
