The 515 MegaPR early downport (#7783)

Co-authored-by: Selis <selis@xynolabs.com>
Co-authored-by: Selis <sirlionfur@hotmail.de>
Co-authored-by: Kashargul <144968721+Kashargul@users.noreply.github.com>
Co-authored-by: SatinIsle <thesatinisle@gmail.com>
Co-authored-by: Heroman <alesha3000@list.ru>
Co-authored-by: Casey <a.roaming.shadow@gmail.com>
Co-authored-by: Raeschen <rycoop29@gmail.com>

code/controllers/subsystems/asset_loading.dm

@@ -0,0 +1,28 @@
+/// Allows us to lazyload asset datums
+/// Anything inserted here will fully load if directly gotten
+/// So this just serves to remove the requirement to load assets fully during init
+SUBSYSTEM_DEF(asset_loading)
+	name = "Asset Loading"
+	priority = FIRE_PRIORITY_ASSETS
+	flags = SS_NO_INIT
+	runlevels = RUNLEVEL_LOBBY|RUNLEVELS_DEFAULT
+	var/list/datum/asset/generate_queue = list()
+
+/datum/controller/subsystem/asset_loading/fire(resumed)
+	while(length(generate_queue))
+		var/datum/asset/to_load = generate_queue[generate_queue.len]
+
+		to_load.queued_generation()
+
+		if(MC_TICK_CHECK)
+			return
+		generate_queue.len--
+
+/datum/controller/subsystem/asset_loading/proc/queue_asset(datum/asset/queue)
+#ifdef DO_NOT_DEFER_ASSETS
+	stack_trace("We queued an instance of [queue.type] for lateloading despite not allowing it")
+#endif
+	generate_queue += queue
+
+/datum/controller/subsystem/asset_loading/proc/dequeue_asset(datum/asset/queue)
+	generate_queue -= queue