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/structures/plaques/_plaques.dm

@@ -20,6 +20,8 @@
 
 /obj/structure/plaque/Initialize(mapload)
 	. = ..()
+	if(mapload)
+		find_and_mount_on_atom()
 	register_context()
 
 /obj/structure/plaque/add_context(atom/source, list/context, obj/item/held_item, mob/user)

code/game/objects/structures/plaques/static_plaques.dm

@@ -9,6 +9,13 @@
 		SET_PLANE_IMPLICIT(src, FLOOR_PLANE)
 		layer = HIGH_TURF_LAYER
 
+/obj/structure/plaque/static_plaque/get_moutable_objects()
+	return list()
+
+/obj/structure/plaque/static_plaque/find_and_mount_on_atom(mark_for_late_init, late_init)
+	if(isProbablyWallMounted(src))
+		return ..()
+
 /obj/structure/plaque/static_plaque/atmos
 	name = "\improper FEA Atmospherics Division plaque"
 	desc = "This plaque commemorates the fall of the Atmos FEA division. For all the charred, dizzy, and brittle men who have died in its hands."