Visual / layering fixes (#19547)

Package of a few visual changes to make things prettier-er. Also added a
helper for mapping purposes.

  - bugfix: "Carpets now show proper edges again."
- bugfix: "Fixed layering of several map items, like disposal pipes,
that were previously buried underneath turfs in the map editor (and were
invisible as a result)."
- bugfix: "Fixed observer sprites occasionally going underneath certain
objects. Their layering has been fixed."
- bugfix: "Reinforced plastic tables now show up correctly in the map
editor."
- rscadd: "Added a special 'lock' door helper that automatically locks
doors underneath it so mappers don't have to edit variables/icon states
manually."


![image](https://github.com/Aurorastation/Aurora.3/assets/55491249/53d97049-0104-491a-9a56-4d677afec536)

![image](https://github.com/Aurorastation/Aurora.3/assets/55491249/a26c9cf6-1ea9-4654-bc5c-954c878efda3)

![image](https://github.com/Aurorastation/Aurora.3/assets/55491249/6dbee17e-6a24-4cc9-b194-4c46530020be)

Fixes #18762 
Fixes #18840 
Fixes #19101

code/modules/recycling/disposal.dm

@@ -794,7 +794,7 @@
 	var/dpdir = 0		// bitmask of pipe directions
 	dir = 0				// dir will contain dominant direction for junction pipes
 	var/health = 10 	// health points 0-10
-	layer = DISPOSALS_PIPE_LAYER
+	layer = EXPOSED_DISPOSALS_PIPE_LAYER
 	var/sortType = ""
 	var/subtype = 0
 	// new pipe, set the icon_state as on map