fix: controlled rotorcrafts shouldn't fall when loosing ground

[Vollch]

Purpose of change

• fixes wheeled helicopter falls down when there's nothing below #3903

Describe the solution

Check whether vehicle is rotorcraft before falling, if so - start flying instead.

Describe alternatives you've considered

Rewriting all flying code, it's a mess with hardcode checks for specific z levels, and tons of bugs. But for now this will work as a quick fix, it's not the best idea to jump into rewriting flying while we're in middle of obsoleting legacy zlevels.

Testing

Flied off deck on wheeled apache from #3901

Additional context

Checklist

[scarf005]

2023-12-15_10-27-52.mp4

it still sinks.

[Vollch]

Apparently vehicles doesn't always "drop", so... I moved that check where it should trigger more reliably.

Also, during re-testing i noticed that is still sinks when flying from bottom deck. That's, kinda, intended, as it doesn't really fall in that case, but goes directly to /dev/null.
Same will happen if you'll try to descent down to water surface at any other moment. Fixing that would require rewriting landing check, which probably require rewriting whole flying detection, and then adding some check to detect submerging... all that will snowball too far for a "quick fix". But for decks at z1 and z2(where helicopters are naturally spawned) it should work with this fix.

[scarf005]

2023-12-15_18-46-20.mp4

LGTM.

tiny bug: rotorcraft flown this way will erroneously warn it will crash when you try to stop the engine even if it's technically landed. at some point we should migrate from is_falling and is_flying to proper state machine with sum types.

[Vollch]

Yeah, i know. That's actually an old bug, one of those "tons of bugs" mentioned in first post.