fix(cdu): correct tmply fpln activation logic in airways page

[robertxing2004]

Summary of Changes

Extension of #9148

The airways page now only creates a tmpy fpln after a valid segment is entered; either an airway and a terminating waypoint, or an airway followed by an intersecting airway. Prior to either of these two conditions being met, there is no pending flight plan, and pressing return will not result in a false tmpy state on the fpln page.

Screenshots (if necessary)

References

Additional context

While troubleshooting this issue, I discovered bugs #9560 and #9561, but as it stands this PR only fixes the tmpy fpln activation logic. Those bugs can be addressed in a separate PR.

Discord username (if different from GitHub):
robeet

Testing instructions

1. Spawn anywhere and start a fpln from the mcdu
2. After entering a STAR and transition, enter the airways page and make modifications
3. Verify that there is no option to erase or insert until a terminating waypoint or intersecting airway has been entered
4. Returning any time before the above two conditions should not create a tmpy fpln

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[BlueberryKing]

How is targetPlan different from currentPlan? Will targetPlan be a temporary plan?

[robertxing2004]

They're the same thing; I originally was not declaring currentPlan, and only declaring targetPlan.

I ran into an issue where if I only assigned const targetPlan = mcdu.flightPlan... once, either at the top or after the startAirwayEntry then the respective results would be that either targetPlan.pendingAirways.thenAirway would be undefined or if (!targetPlan.pendingAirways) {...} would be undefined.

I'm pretty sure it's because const targetPlan = mcdu.flightPlan... needs to be assigned after mcdu.flightPlanService.startAirwayEntry(prevFpIndex, forPlan, inAlternate); or it won't pick up the new pending airway entry. At the same time though, if I don't assign mcdu.flightPlan before doing if (!targetPlan.pendingAirways) {...} then that if statement is undefined because targetPlan is shadowed under mcdu.onLeftInput and out of scope of mcdu.onRightInput.

Of course, I can't use the same variable name twice here if I'm reassigning, hence the two different names, and I'm admittedly not seeing a way of preserving the logic without redeclaring the variable.