Refactor /obj/screen to /atom/movable/screen (#19852)

Part of backend stuff required for #19188. Should probably be test
merged.

---------

Co-authored-by: Cody Brittain <cbrittain10@live.com>

code/modules/psionics/interface/ui.dm

@@ -1,14 +1,14 @@
-/obj/screen/psi
+/atom/movable/screen/psi
 	icon = 'icons/mob/screen/psi.dmi'
 	var/mob/living/owner
 	var/hidden = TRUE
 
-/obj/screen/psi/New(var/mob/living/_owner)
+/atom/movable/screen/psi/New(var/mob/living/_owner)
 	loc = null
 	owner = _owner
 	update_icon()
 
-/obj/screen/psi/Destroy()
+/atom/movable/screen/psi/Destroy()
 	if(owner && owner.client)
 		owner.client.screen -= src
 	. = ..()