Falling speed should be capped

I noticed this while initially working on a research for #8925, but shoved it aside without a second thought since I figured it isn't related to projectiles specifically, and is probably already in the game.

But after the gravity incident I decided to double check, just in case. And nope, no trace of it in code.

Basically the limit should equal to -4005.5. This is confirmed in this discord message. With usual gravity, it only affects falls longer than ~6.4 s, so Icarian scrolls and all that.

Steps to reproduce

OpenMW

1. Player->Position 0 0 40000 0
2. Start your stopwatch as soon as you close the console.
3. Stop it when you hit the ground.

Vanilla, 60 FPS

1. Player->Position 0 0 0 0
2. Player->AddItem "p_levitation_e" 1
3. Player->Equip "p_levitation_e"
4. Player->SetPos z 40000
5. Player->RemoveEffects 10
6. Start your stopwatch as soon as you close the console.
7. Stop it when you hit the ground.

In OpenMW, it should be around ~11.32 s. In vanilla, it should be around ~13.18 s.