Stairs DLC: Buildable stairs, material datum staircases, fall up a staircase (#70504)

Adds a few new types of stairs, and makes stairs buildable within rounds.
Also removes the terminator sprite variation for stairs, because its basically unused and really not needed with plane cube multiz.

code/controllers/subsystem/materials.dm

@@ -31,6 +31,7 @@ SUBSYSTEM_DEF(materials)
 	///List of stackcrafting recipes for materials using rigid recipes
 	var/list/rigid_stack_recipes = list(
 		new /datum/stack_recipe("Carving block", /obj/structure/carving_block, 5, one_per_turf = TRUE, on_solid_ground = TRUE, applies_mats = TRUE),
+		new /datum/stack_recipe("Material Stairs", /obj/structure/stairs/material, 10, time = 10 SECONDS, one_per_turf = TRUE, on_solid_ground = TRUE, applies_mats = TRUE),
 	)
 
 ///Ran on initialize, populated the materials and materials_by_category dictionaries with their appropiate vars (See these variables for more info)