Shift certain flying mob positions upon death (#85942)

## About The Pull Request

Chasing more side effects of offsetting mobs and giving them shadows.


![dreamseeker_dd0UwOHLV6](https://github.com/user-attachments/assets/1f619084-77f4-41d8-9d0c-eacd63bbf58c)
Some mobs are "flying" while they are alive, but not while they are
dead.
Some mobs (like Watchers) offset their death sprites in the dmi to make
it look like they have dropped to the ground, others do not bother.

For the ones which don't, we want to shift them down ourselves so it
doesn't look like the corpse is levitating.

I'm willing to accept better suggestions for how to implement this but
this seemed like the most obvious.

## Why It's Good For The Game

No more levitating corpses

## Changelog

🆑
fix: Carp, bat, parrot, and dragon corpses no longer float in the air.
/🆑

code/modules/mob/living/basic/basic.dm

@@ -97,6 +97,8 @@
 	var/unsuitable_cold_damage = 1
 	///This damage is taken when the body temp is too hot. Set both this and unsuitable_cold_damage to 0 to avoid adding the body_temp_sensitive element.
 	var/unsuitable_heat_damage = 1
+	///Amount to increment our vertical position by when dead
+	var/death_offset_y = 0
 
 /mob/living/basic/Initialize(mapload)
 	. = ..()
@@ -123,6 +125,18 @@
 	apply_temperature_requirements(mapload)
 	apply_target_randomisation()
 
+/mob/living/basic/create_shadow()
+	if (shadow_type == SHADOW_NONE)
+		qdel(GetComponent(/datum/component/drop_shadow))
+		return
+
+	AddComponent(/datum/component/drop_shadow, \
+		icon_state = shadow_type, \
+		shadow_offset_x = shadow_offset_x, \
+		shadow_offset_y = shadow_offset_y, \
+		death_offset = -death_offset_y, \
+	)
+
 /mob/living/basic/proc/on_ssair_init(datum/source)
 	SIGNAL_HANDLER
 	UnregisterSignal(SSair, COMSIG_SUBSYSTEM_POST_INITIALIZE)
@@ -189,6 +203,7 @@
 	if(!(basic_mob_flags & REMAIN_DENSE_WHILE_DEAD))
 		ADD_TRAIT(src, TRAIT_UNDENSE, BASIC_MOB_DEATH_TRAIT)
 	SEND_SIGNAL(src, COMSIG_BASICMOB_LOOK_DEAD)
+	pixel_z = base_pixel_z + death_offset_y
 
 /mob/living/basic/revive(full_heal_flags = NONE, excess_healing = 0, force_grab_ghost = FALSE)
 	. = ..()
@@ -204,6 +219,8 @@
 	if(!(basic_mob_flags & REMAIN_DENSE_WHILE_DEAD))
 		REMOVE_TRAIT(src, TRAIT_UNDENSE, BASIC_MOB_DEATH_TRAIT)
 	SEND_SIGNAL(src, COMSIG_BASICMOB_LOOK_ALIVE)
+	if (death_offset_y != 0)
+		pixel_z = base_pixel_z
 
 /mob/living/basic/update_sight()
 	lighting_color_cutoffs = list(lighting_cutoff_red, lighting_cutoff_green, lighting_cutoff_blue)
@@ -247,6 +264,8 @@
 		if(NAMEOF(src, speed))
 			datum_flags |= DF_VAR_EDITED
 			set_varspeed(vval)
+		if(NAMEOF(src, death_offset_y))
+			create_shadow()
 
 /mob/living/basic/proc/set_varspeed(var_value)
 	speed = var_value