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/modules/library/lib_items.dm

@@ -21,7 +21,7 @@
 	desc = "A great place for storing knowledge."
 	anchored = FALSE
 	density = TRUE
-	opacity = 0
+	opacity = FALSE
 	resistance_flags = FLAMMABLE
 	max_integrity = 200
 	armor = list("melee" = 0, "bullet" = 0, "laser" = 0, "energy" = 0, "bomb" = 0, "bio" = 0, "rad" = 0, "fire" = 50, "acid" = 0)