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/effects/effect_system/effects_explosion.dm

@@ -1,7 +1,7 @@
 /obj/effect/particle_effect/expl_particles
 	name = "fire"
 	icon_state = "explosion_particle"
-	opacity = 1
+	opacity = TRUE
 	anchored = TRUE
 
 /obj/effect/particle_effect/expl_particles/Initialize()
@@ -27,7 +27,7 @@
 	name = "fire"
 	icon = 'icons/effects/96x96.dmi'
 	icon_state = "explosion"
-	opacity = 1
+	opacity = TRUE
 	anchored = TRUE
 	mouse_opacity = MOUSE_OPACITY_TRANSPARENT
 	pixel_x = -32

code/game/objects/effects/effect_system/effects_foam.dm

@@ -8,7 +8,7 @@
 /obj/effect/particle_effect/foam
 	name = "foam"
 	icon_state = "foam"
-	opacity = 0
+	opacity = FALSE
 	anchored = TRUE
 	density = FALSE
 	layer = EDGED_TURF_LAYER
@@ -257,7 +257,7 @@
 	icon = 'icons/effects/effects.dmi'
 	icon_state = "metalfoam"
 	density = TRUE
-	opacity = 1 	// changed in New()
+	opacity = TRUE 	// changed in New()
 	anchored = TRUE
 	layer = EDGED_TURF_LAYER
 	resistance_flags = FIRE_PROOF | ACID_PROOF

code/game/objects/effects/effect_system/effects_smoke.dm

@@ -8,7 +8,7 @@
 	icon_state = "smoke"
 	pixel_x = -32
 	pixel_y = -32
-	opacity = 0
+	opacity = FALSE
 	layer = FLY_LAYER
 	anchored = TRUE
 	mouse_opacity = MOUSE_OPACITY_TRANSPARENT