Aft remap refactoring (#21555)

# Summary

This PR refactors some areas changed in the recent Aft-remap. This one
focuses mainly on atmos and the areas around in.

## Changes

- Added missing tiling below grates in different places
- Refactor new mixing tank console/ventilation settings
- Shuffles atmos locker room around
- Add atmos locker maintenance area
- Refactors atmos (lights, decals, wall mount, new default scrubbing
pump/valve)
- Refactors atmos mixing (lights, decals, wall mount, new default atmos
supply regulator)
- Refactors D1 hallway in front of atmos
- Refactors maintenance areas around previously mentioned areas
- Fixes missing wire in the commissary
- Fixes meta area definition for engineering hardstorage
- Misc. fixes/refactoring

In general, nothing big, the expected cleanup after a big remap.

Thanks to @Batrachophreno for the big work.

html/changelogs/fabiank3-aft-remap-refactoring.yml

@@ -0,0 +1,7 @@
+author: FabianK3
+
+delete-after: True
+
+changes:
+  - rscadd: "Added a storage maintenance room behind the atmos locker room."
+  - qol: "Refactoring of multiple places after aft remap changes."

maps/sccv_horizon/areas/horizon_areas_engineering.dm

@@ -124,6 +124,14 @@
 	area_blurb = "The softly reassuring sounds of churning humming whirring resound gently from the distribution control compartment below."
 	horizon_deck = 2
 
+/area/horizon/engineering/atmos/storage_maintenance
+	name = "Atmos Storage maintenance"
+	icon_state = "atmos_storage"
+	sound_environment = SOUND_AREA_SMALL_ENCLOSED
+	area_blurb = "The metal clanking of pipes being jostled; gas canister telltales blinking out from corners. \
+	It's as organized as you would expect a hidden away storage to be."
+	horizon_deck = 2
+
 /area/horizon/engineering/atmos/air
 	name = "Air Mixing"
 

maps/sccv_horizon/areas/horizon_areas_maintenance.dm

@@ -128,6 +128,9 @@
 /area/horizon/maintenance/deck_2/cargo_compartment
 	name = "Auxiliary Cargo Maintenance"
 
+/area/horizon/maintenance/deck_2/elevator
+	name = "Elevator Maintenance"
+
 /area/horizon/maintenance/deck_2/central_ring
 	name = "Central Ring Maintenance"