Refactor chasm paths to be more sane (#32701)

In addition, makes chasm handling a component, so it could be reused for
chasm-likes which are not quite chasms.

Also fixes a couple of bugs relating to building on top of chasms
occasionally erasing the chasm.

_maps/RandomRuins/LavaRuins/lavaland_biodome_clown_planet.dmm

@@ -1,4 +1,4 @@
-//MAP CONVERTED BY dmm2tgm.py THIS HEADER COMMENT PREVENTS RECONVERSION, DO NOT REMOVE 
+//MAP CONVERTED BY dmm2tgm.py THIS HEADER COMMENT PREVENTS RECONVERSION, DO NOT REMOVE
 "aa" = (
 /turf/template_noop,
 /area/template_noop)
@@ -848,7 +848,7 @@
 	},
 /area/lavaland/surface/outdoors/explored)
 "gX" = (
-/turf/open/chasm/straight_down/lava_land_surface,
+/turf/open/chasm/lavaland,
 /area/lavaland/surface/outdoors/explored)
 "hY" = (
 /obj/machinery/light,

_maps/shuttles/emergency_clown.dmm

@@ -110,7 +110,7 @@
 /turf/closed/wall/mineral/titanium,
 /area/shuttle/escape)
 "au" = (
-/turf/open/chasm/straight_down/lava_land_surface/normal_air,
+/turf/open/chasm,
 /area/shuttle/escape)
 "av" = (
 /obj/machinery/light{