Tiny Combat Arena - Improved Explosion Handling

Getting hit by one of the SA-2s blew up all the parts on the plane at the same time. It looked weird, felt wrong, and wasn't any fun, so I spent almost all yesterday going through the explosion code. There were quite a few bugs that had gone unnoticed because they only affected the planes with complex damage models. Explosions now act much more consistently with how you'd expect them to, and getting hit by a missile is way more fun.

Aside from some fixes which were just bug fixes, the two big changes were:

Falloff damage - Damage taken by an explosion falls off depending on distance to the explosion. There's also a minimum distance where anything inside it takes full damage (dotted lines). Pretty straightforward, but it wasn't in the game before since it wasn't needed.

Hit limit - In the previous system, if an explosion encompassed an entire plane, then all parts of the plane were damaged. This makes some logical sense, but it doesn't feel right when a missile explodes to the left of a plane, but takes off the right wing. In the new system, only the two nearest hits are considered. Exploding to the left of the plane now means only the left wingtip, and wing center (in the Harrier's case) are damaged. Since all damage to subparts propagates up to the plane, this also makes damage a lot predictable since it's always 2 parts at most. Planes with many subparts (E.g. Su-25) could previously take as much as 6X damage in a single hit because its wings were made up of so many parts.

Ironically all that work yesterday fixing how explosions and the aircraft damage model interact, broke vehicle's taking damage from explosions. An explosion near a vehicle crashes the game now. That's game development for you. ¯\_(ツ)_/¯