Overcoming Verticality - Adds ramps, extends the medical lift and fixes stair gravity. (#19182)

Adds ramps, which function as dummy verticality like many of the stairs,
except they don't trigger the "Stairs are dangerous" response, allowing
certain areas to be more accessible.

Extends the medical lift to deck three, allowing a non-stair based way
to reach the upper department.

Fixes the "Stairs are dangerous" interaction not checking for gravity.

---------

Signed-off-by: Matt Atlas <mattiathebest2000@hotmail.it>
Co-authored-by: Matt Atlas <mattiathebest2000@hotmail.it>

code/modules/multiz/structures.dm

@@ -276,7 +276,7 @@
 				playsound(target, 'sound/effects/stairs_step.ogg', 50)
 
 /obj/structure/stairs/Crossed(obj/O)
-	if(istype(O))
+	if(istype(O) && has_gravity(get_turf(src)))
 		O.stair_act()
 	return ..()
 
@@ -376,9 +376,13 @@
 	anchored = TRUE
 	icon = 'icons/obj/structure/stairs.dmi'
 	icon_state = "np_stair"
+	/**
+	 * If true, this strucutre will trigger the stairs_act() proc for other structures being moved across it.
+	 */
+	var/steps = TRUE
 
 /obj/structure/platform_stairs/Crossed(obj/O)
-	if(istype(O))
+	if(istype(O) && has_gravity(get_turf(src)) && steps)
 		O.stair_act()
 	return ..()
 
@@ -400,6 +404,18 @@
 /obj/structure/platform_stairs/full/south_north_cap/half
 	icon_state = "p_stair_sn_half_cap"
 
+/obj/structure/platform_stairs/ramp
+	name = "ramp"
+	desc = "A smooth yet archaic form of locomotion along the vertical axis."
+	steps = FALSE
+	layer = ABOVE_TILE_LAYER //They sit ontop of turfs, but below most other things
+
+/obj/structure/platform_stairs/ramp/north_south
+	icon_state = "p_ramp_sn_full_cap"
+
+/obj/structure/platform_stairs/ramp/east_west
+	icon_state = "p_ramp_ew_full_cap"
+
 /obj/structure/platform
 	name = "platform"
 	desc = "An archaic method of preventing travel along the X and Y axes if you are on a lower point on the Z-axis."