Dir assist now prioritises non-xenos (#6461)

# About the pull request
This PR makes it so when using dir assist against a xeno and a non-xeno
on the same tile the attack will prioritize the non-xeno over the xeno.
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# Explain why it's good for the game
You are more likely to want to target the marine than shove\slash the
xeno ontop of the marine.
It is annoying when John runner stands ontop of the guy you are
currently pulling and now you have to click the 3 remaining pixels
visible.
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
qol: Dir-assist will now prioritize non-xenos over xenos.
/:cl:

code/_onclick/xeno.dm

@@ -13,6 +13,7 @@
 
 	if(isturf(target) && tile_attack) //Attacks on turfs must be done indirectly through directional attacks or clicking own sprite.
 		var/turf/T = target
+		var/mob/living/non_xeno_target
 		for(var/mob/living/L in T)
 			if (!iscarbon(L))
 				if (!alt)
@@ -21,13 +22,19 @@
 
 			if (!L.is_xeno_grabbable() || L == src) //Xenos never attack themselves.
 				continue
+			var/isxeno = isxeno(L)
+			if(!isxeno)
+				non_xeno_target = L
 			if (L.body_position == LYING_DOWN)
 				alt = L
 				continue
+			else if (!isxeno)
+				break
 			target = L
-			break
 		if (target == T && alt)
 			target = alt
+		if(non_xeno_target)
+			target = non_xeno_target
 		if (T && ignores_resin) // Will not target resin walls and doors if this is set to true. This is normally only set to true through a directional attack.
 			if(istype(T, /obj/structure/mineral_door/resin))
 				var/obj/structure/mineral_door/resin/attacked_door = T