moves abstract_type up to datum, spawners wont spawn them (#92909)

## About The Pull Request
moves all implementations (im aware of) for "Im a parent type dont spawn
me please" to the datum layer to standardized behavior
adds a standerized proc for filtering out "bad" items that we dont want
spawning. applies to it the subtype vendor, gifts, and a new spawner and
mystery box for a random gun (neither playerfacing)
"port" of https://github.com/shiptest-ss13/Shiptest/pull/4621



https://github.com/user-attachments/assets/22f6f0b2-b44e-411a-b3dc-6b97dc0287aa

small warning: I dont have EVERY abstract type defined right now but,
ive done a good enough job for now. Im tired of data entry rn
## Why It's Good For The Game
standardizing behavior. Might be a micro hit to performance however

having this lets us not rely on icon state to determine whether
something is a parent type and makes it much easier to tell something is
a parent type (could be applied further to things like admin spawning
menus and things like that).

need feedback on if this is actually good for the game.
## Changelog
🆑
add: Soda cans show up in the silver slime drink table.
add: Examine tag for items that are not mean to show up ingame.
refactor: Standardizes how gifts rule out abstract types.
fix: gifts no longer check if something has an inhand, massively
expanding the list of potential items.
/🆑

code/modules/vending/subtype.dm

@@ -22,7 +22,7 @@
 ///Adds the subtype to the product list
 /obj/machinery/vending/subtype_vendor/RefreshParts()
 	products.Cut()
-	for(var/type in typesof(type_to_vend))
+	for(var/type in get_sane_item_types(type_to_vend))
 		LAZYADDASSOC(products, type, 50)
 
 	//no refill canister so we fill the records with their max amounts directly

code/modules/vending/vendor/_vending.dm

@@ -38,6 +38,7 @@
 	desc = "A generic vending machine."
 	icon = 'icons/obj/machines/vending.dmi'
 	icon_state = "generic"
+	abstract_type = /obj/machinery/vending
 	layer = BELOW_OBJ_LAYER
 	density = TRUE
 	verb_say = "beeps"