TankNut: no Lua equivalent of PhysicsImpact for physics-driven player movement

In #developer-talk, TankNut described problems with his physics-driven mech: movement is unpredicted, so multiplayer feels slow, and hook order breaks things because the mech moves in PhysicsUpdate after its turrets update in PlayerPostThink/Think. He added that the biggest problem in recreating player movement is that Lua has no equivalent of entity->PhysicsImpact, though ApplyForceOffset might be enough. He later said it may matter less, since it seems to be only for touch-related things.