Fix xeno wounds layering over weeded xenos (#5289)

# About the pull request

This PR is a follow up to #5118 to fix the xeno wounds object appearing
above their weeded appearance. It now synchronizes its plane and layer
with the mob using vis_flags.

# Explain why it's good for the game

Fixes (defender near wall):

![image](https://github.com/cmss13-devs/cmss13/assets/76988376/186acf03-c686-4114-9d53-c82687e0129c)

Fixes (drone under door):

![image](https://github.com/cmss13-devs/cmss13/assets/76988376/49301147-d1cd-49fc-b977-df2c446cdf45)


# Testing Photographs and Procedure

![image](https://github.com/cmss13-devs/cmss13/assets/76988376/e5c4d69b-e9a3-429b-a2d5-e7a5915c5fee)

# Changelog
:cl: Drathek
fix: Fix xeno wounds layering over weeds when merged with the weeds
/:cl:

code/modules/mob/living/carbon/xenomorph/update_icons.dm

@@ -301,7 +301,6 @@
 		return
 
 	var/health_threshold
-	wound_icon_holder.layer = layer + 0.01
 	health_threshold = max(CEILING((health * 4) / (maxHealth), 1), 0) //From 0 to 4, in 25% chunks
 	if(health > HEALTH_THRESHOLD_DEAD)
 		if(health_threshold > 3)
@@ -316,10 +315,9 @@
 		else
 			wound_icon_holder.icon_state = handle_special_wound_states(health_threshold)
 
-
 ///Used to display the xeno wounds/backpacks without rapidly switching overlays
 /atom/movable/vis_obj
-	vis_flags = VIS_INHERIT_ID|VIS_INHERIT_DIR
+	vis_flags = VIS_INHERIT_ID|VIS_INHERIT_DIR|VIS_INHERIT_LAYER|VIS_INHERIT_PLANE
 	appearance_flags = RESET_COLOR
 
 /atom/movable/vis_obj/xeno_wounds