Readds Alien Vore (#68312)

* Readds Alien Vore

Aliens can now eat people again. Behavior was removed by #43991 (b6c41e3b32)
because nasku thought it was weird, and the code was really bad.

I think it's funny, and I've made the code not trashtier.

Basically, an alien can agressive grab any living mob. If they stay next
to the mob, facing them for 13 seconds, they will "eat" the mob,
IE:insert them into a list on their custom stomach.

The xeno can then hit an action button to spit out the mob, alongside
some acid.

If the mob is alive enough to pull out a weapon inside the xeno/has one
on it, they can attack the xeno from inside, dealing damage to the
creature and its stomach. If the stomach drops below a threshold, the
mob gibs the xeno and escapes.

I've done my best to steer things away from horny and into gross, though
I'm aware you fucks do your best to blur that line.

Anyway something something balance change something something lets xenos
abduct people more easily, I'm mostly doing this cause I think it has
soul.

Co-authored-by: MrMelbert <51863163+MrMelbert@users.noreply.github.com>

code/game/objects/effects/effect_system/effects_water.dm

@@ -7,7 +7,6 @@
 	var/life = 15
 	mouse_opacity = MOUSE_OPACITY_TRANSPARENT
 
-
 /obj/effect/particle_effect/water/Initialize(mapload)
 	. = ..()
 	QDEL_IN(src, 70)
@@ -58,6 +57,17 @@
 	QDEL_IN(src, engine.delay) //Gotta let it stop drifting
 	animate(src, alpha = 0, time = engine.delay)
 
+/obj/effect/particle_effect/water/extinguisher/stomach_acid
+	name = "acid"
+	icon_state = "xenobarf"
+
+// Stomach acid doesn't use legacy because it's not "targeted", and we instead want the circular sorta look
+/obj/effect/particle_effect/water/extinguisher/stomach_acid/move_at(atom/target, delay, lifetime)
+	var/datum/move_loop/loop = SSmove_manager.move_towards(src, target, delay, timeout = delay * lifetime, flags = MOVEMENT_LOOP_START_FAST, priority = MOVEMENT_ABOVE_SPACE_PRIORITY)
+	RegisterSignal(loop, COMSIG_MOVELOOP_POSTPROCESS, .proc/post_forcemove)
+	RegisterSignal(loop, COMSIG_PARENT_QDELETING, .proc/movement_stopped)
+	return loop
+
 /////////////////////////////////////////////
 // GENERIC STEAM SPREAD SYSTEM