Implements Cardinal Smoothing Support, Misc Smoothing Cleanup (#84402)

## About The Pull Request

[Implements a new cardinal only bitmask smoothing
mode](https://github.com/tgstation/tgstation/commit/d56556491813657e5ba794ec856649f01291c39a)

The icon cutter supports generating cardinal only dmis, we should
support using them.

This is fairly trivial, just involves skipping a step to handle
diagonals.

While I'm here, makes adding new smoothing modes easier by creating a
"using smoothing" group define

[Removes undef for smoothing
junctions](https://github.com/tgstation/tgstation/pull/84402/commits/4c0a4d6e34f79769ab20c989620f396f4b4a3fe0)

It is useful to be able to reference these in the general codebase, they
should not be considered scoped to just icon smoothing

[Fixes a copypasta issue breaking burn states for asteroid
snow](https://github.com/tgstation/tgstation/commit/a41b31dbe21676aa95cb6a625d8f4deb3233faba)

[Removes SMOOTH_BROKEN_TURF and
SMOOTH_BURNT_TURF](https://github.com/tgstation/tgstation/commit/8a9a340728680b2988abd19631495e955de9ebf1)

Bitflags should not be this specific, this should be a var on
/turf/open, so that's what I'm making it.

## Why It's Good For The Game

Upstreams a bit of wallening work, cleans up the codebase some

## Changelog
🆑
fix: Some varieties of snow now visually melt properly again when burned
/🆑

code/game/objects/structures.dm

@@ -19,7 +19,7 @@
 
 /obj/structure/Initialize(mapload)
 	. = ..()
-	if(smoothing_flags & (SMOOTH_CORNERS|SMOOTH_BITMASK))
+	if(smoothing_flags & USES_SMOOTHING)
 		QUEUE_SMOOTH(src)
 		QUEUE_SMOOTH_NEIGHBORS(src)
 		if(smoothing_flags & SMOOTH_CORNERS)
@@ -28,7 +28,7 @@
 
 /obj/structure/Destroy(force)
 	GLOB.cameranet.updateVisibility(src)
-	if(smoothing_flags & (SMOOTH_CORNERS|SMOOTH_BITMASK))
+	if(smoothing_flags & USES_SMOOTHING)
 		QUEUE_SMOOTH_NEIGHBORS(src)
 	return ..()