LV-624 Cave Aesthetic Change (#4843)

# About the pull request

Alters the caves of LV-624 to have far more jungle grass and other
similar aesthetics. No layout changes are effected.

I hope to do more changes in the future, but I'll keep things separated
for now.

# Explain why it's good for the game

The caves of the map are quite bare in appearance, this is one small
chance to help increase the style of the map.


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
maptweak: LV-624's Caves have had an aesthetic change regarding jungle
tiles and flora.
/:cl:

Co-authored-by: Steelpoint <[email protected]>

code/game/objects/effects/decals/warning_stripes.dm

@@ -91,6 +91,20 @@
 /obj/effect/decal/sand_overlay/sand2/corner2
 	icon_state = "sand2_c"
 
+/obj/effect/decal/grass_overlay
+	name = "grass edge"
+	mouse_opacity = MOUSE_OPACITY_TRANSPARENT
+	unacidable = TRUE
+	icon = 'icons/turf/floors/auto_strata_grass.dmi'
+	layer = TURF_LAYER
+
+/obj/effect/decal/grass_overlay/grass1
+	icon_state = "grass_outercorner"
+
+/obj/effect/decal/grass_overlay/grass1/inner
+	name = "grass edge"
+	icon_state = "grass_innercorner"
+
 /obj/effect/decal/siding
 	name = "siding"
 	icon = 'icons/turf/floors/floors.dmi'