Persistent trash (#21217)

# Summary

This PR adds trash to the persistence system.

- Trash becomes persistent the moment it is dropped unless it is dropped
in a maint or the disposal room.
- It looses persistence when it lands in a maint/disposal room or gets
picked up again.
- Persistent trash can be found up to three days.

Those are the base rules, some trash types have additional rules.

List of trash to be implemented:

- [x] Basic trash (snacks and such)
  - Cigarette buts
  - spitwad
  - Burned matches
- [x] Broken bottles
- [x] Torn inflatable (-doors)

> Littering is a i120 violation and can be punished with 3-7 minutes of
prison time or with a 40-150 credit fine.
> Stop littering and keep the ship clean.

## Follow-up tasks

- [x] Update GitHub Wiki: Add section on how to add persistent trash
types.
- [x] Update GitHub Wiki: Make persistence_get_content nullable/empty.

code/modules/mapping/reader.dm

@@ -543,6 +543,7 @@ GLOBAL_LIST_INIT(_preloader_path, null)
 /area/template_noop
 	name = "Area Passthrough"
 	icon_state = "noop"
+	area_flags = AREA_FLAG_PREVENT_PERSISTENT_TRASH
 
 /turf/template_noop
 	name = "Turf Passthrough"