Multiplayer: Separate synced animation state from local rendering state

[rainlizard]

There's an issue with the animation variables on an individual creature being treated as local variables, while they're actually supposed to be synced. They're being shared between players, because there's only one creature with one set of variables.

I'll just lead with the obvious here: animation variables need to be synced because there's a lot of gameplay stuff tied to them.

They changed locally whenever you switched views. So in multiplayer when a resync happens they get copied from the host machine, which apparently can cause a permanent resync loop. When you switch between first person view and top down view, the current_frame and max_frames inside creatures change, which might have you wondering: Which player's current view owns the thing->current_frame? In multiplayer each machine can have a different local view (someone can be in first person and someone can be in top down view), but they are still utilizing these same shared variables on the same creature which isn't very safe.

One partial solution would be to simply not checksum current_frame and max_frames, which is what we've mostly been doing, but I'm pretty sure that's just hiding the issue away and results in obscure butterfly-effect desyncs down the line.

Anyway what I've done here: Inside a Thing/creature, the anim_sprite/anim_speed/anim_time/current_frame/max_frames variables now all consistently refer to the top down values, but during render time this is converted to the first-person values (if player is in first person view). This "conversion" doesn't mean setting the values, it's just local to the rendering code.