Standing on structures such as crates, tables and bed will now look like it. (#79797)

## About The Pull Request
From the creator of 'cosmetic' elements such as footstep_override and
immerse...

I've made an element called elevation that nudges mobs a few pixels up
while standing on things like tables, crates and beds.

Screenshots of many clones of the same character standing on different
objects:
![the clone
army](https://github.com/tgstation/tgstation/assets/42542238/43ecdc25-f0d2-47fd-96dc-acafcf63483c)

## Why It's Good For The Game
It makes it look like the mob is actually standing on an elevated
surface.

## Changelog

🆑
add: Standing on structures such as crates, tables and bed will now look
like it.
/🆑

code/game/objects/structures/transit_tubes/transit_tube.dm

@@ -20,6 +20,7 @@
 	init_tube_dirs()
 	update_appearance()
 	AddElement(/datum/element/climbable)
+	AddElement(/datum/element/elevation, pixel_shift = 12)
 
 /obj/structure/transit_tube/Destroy()
 	for(var/obj/structure/transit_tube_pod/P in loc)