Enhances algorithm for finding an atom mount (#94076)

## About The Pull Request
Depends on #94064 for the unit test but offers a better method for
finding an atom to mount on
- Finding a mount now takes into consideration the objects pixel x & y
offsets meaning diagonal mounting is now supported. Gives great
flexibility for mappers
- If you don't want to use pixel offsets but default back to using the
objects direction that behaviour is still preserved. Useful if your
object uses directional icon states(lights & cameras for now) AND don't
use offsets
- If no direction could be specified then as the last resort it defaults
back to the objects local turf for mounting

## Changelog
🆑
fix: all mounted objects on tables, fences, windows & walls should fall
of correctly when the atom it is placed on is destroyed
fix: security telescreen now falls off when their mounted wall is
destroyed
fix: defib wall mount falls off when their mounted wall is destroyed
fix: floor lights are mounted to the ground/catwalk/tram floor they are
sitting on meaning destroying it will destroy the light
fix: wall mounted plaques now fall off when their mounted wall is
destroyed
/🆑

code/game/objects/items/devices/radio/intercom.dm

@@ -39,7 +39,7 @@
 		return
 	RegisterSignal(current_area, COMSIG_AREA_POWER_CHANGE, PROC_REF(AreaPowerCheck))
 	if(mapload)
-		find_and_hang_on_atom()
+		find_and_mount_on_atom()
 	GLOB.intercoms_list += src
 
 /obj/item/radio/intercom/Destroy()

code/game/objects/items/wall_mounted.dm

@@ -52,7 +52,7 @@
 				hanging_object.pixel_x = pixel_shift
 			if(WEST)
 				hanging_object.pixel_x = -pixel_shift
-	if(!hanging_object.find_and_hang_on_atom())
+	if(!hanging_object.find_and_mount_on_atom())
 		to_chat(user, span_warning("[src] Could not find all to mount on!."))
 		return
 	after_attach(hanging_object)