Opacity refactor (#52881)

Moves all opacity var manipulation to a proc which sends a signal.
    light_blocker element for movable opaque atoms made, which tracks its movement and updates the affected turfs for proper lighting updates.
    has_opaque_atom boolean replaced by the opacity_sources lazylist to keep track of the sources, and a directional_opacity which serves a similar function but also allows for future expansion with on-border opaque objects (not yet implemented).
    Some opacity-related sight procs optimized as a result of this.
    Some variables moved to the object's definition.
    A define or two added into the mix for clarity.
    Some code cleaning, like turning booleans into their defines.
    One file renamed for clarity.

Changelog

cl
balance: Mechs no longer block sight. It's a non-trivial cost for the lighting system with little to no gain.
/cl

code/game/objects/structures/fluff.dm

@@ -7,7 +7,7 @@
 	icon_state = "minibar"
 	anchored = TRUE
 	density = FALSE
-	opacity = 0
+	opacity = FALSE
 	var/deconstructible = TRUE
 
 /obj/structure/fluff/attackby(obj/item/I, mob/living/user, params)
@@ -261,4 +261,4 @@
 	deconstructible = FALSE
 
 /obj/structure/fluff/hedge/opaque //useful for mazes and such
-	opacity = 1
+	opacity = TRUE