Function overloads condensation (#18939)

Unified most of the procs into one definition, so there are no duplicate
around the codebase.
Marked some of the above as overridable if a good enough case can be
made for them (eg. external dependency or unlikely to be used).

code/controllers/subsystems/processing/airflow.dm

@@ -15,6 +15,7 @@ PROCESSING_SUBSYSTEM_DEF(airflow)
 	priority = SS_PRIORITY_AIRFLOW
 
 /datum/controller/subsystem/processing/airflow/fire(resumed = FALSE)
+	CAN_BE_REDEFINED(TRUE)
 	if (!resumed)
 		currentrun = processing.Copy()	// Defined in parent.
 

code/controllers/subsystems/processing/nanoui.dm

@@ -8,9 +8,6 @@ PROCESSING_SUBSYSTEM_DEF(nanoui)
 	// NanoUI stuff.
 	var/list/open_uis = list()
 
-/datum/controller/subsystem/processing/nanoui/New()
-	NEW_SS_GLOBAL(SSnanoui)
-
 /**
  * Get an open /nanoui ui for the current user, src_object and ui_key and try to update it with data
  *

code/controllers/subsystems/processing/ntsl2.dm

@@ -140,6 +140,7 @@ PROCESSING_SUBSYSTEM_DEF(ntsl2)
 
 
 /datum/controller/subsystem/processing/ntsl2/fire(resumed)
+	CAN_BE_REDEFINED(TRUE)
 	for(var/task_id in tasks)
 		var/task = tasks[task_id]
 		var/datum/http_request/req = task["request"]

code/controllers/subsystems/processing/obj_tab_items.dm

@@ -7,6 +7,7 @@ PROCESSING_SUBSYSTEM_DEF(obj_tab_items)
 // I know this is mostly copypasta, but I want to change the processing logic
 // Sorry bestie :(
 /datum/controller/subsystem/processing/obj_tab_items/fire(resumed = FALSE)
+	CAN_BE_REDEFINED(TRUE)
 	if (!resumed)
 		currentrun = processing.Copy()
 	//cache for sanic speed (lists are references anyways)

code/controllers/subsystems/processing/psi.dm

@@ -15,6 +15,7 @@ PROCESSING_SUBSYSTEM_DEF(psi)
 	var/list/all_psi_complexes = list()
 
 /datum/controller/subsystem/processing/psi/fire(resumed)
+	CAN_BE_REDEFINED(TRUE)
 	..()
 	if((world.time >= (last_nlom_awareness_check + 30 MINUTES)) && !checking_nlom && !completing_nlom)
 		checking_nlom = TRUE

code/controllers/subsystems/processing/tgui.dm

@@ -26,8 +26,7 @@ PROCESSING_SUBSYSTEM_DEF(tgui)
 	/// The HTML base used for all UIs.
 	var/basehtml
 
-/datum/controller/subsystem/processing/tgui/New()
-	NEW_SS_GLOBAL(SStgui)
+/datum/controller/subsystem/processing/tgui/PreInit()
 	basehtml = file2text('tgui/public/tgui.html')
 	// Inject inline polyfills
 	var/polyfill = file2text('tgui/public/tgui-polyfill.min.js')
@@ -43,6 +42,7 @@ PROCESSING_SUBSYSTEM_DEF(tgui)
 	return ..()
 
 /datum/controller/subsystem/processing/tgui/fire(resumed = FALSE)
+	CAN_BE_REDEFINED(TRUE)
 	if(!resumed)
 		src.current_run = open_uis.Copy()
 	// Cache for sanic speed (lists are references anyways)