Replace most (if not all) output << operators with to_chat(user, message)

Currently, to_chat is literally just a proc that does user << message.
But it'll let us do output modification in the future, especially for
something like Goon's HTML chat.

Big thanks to PJB for his to_chat script, see
https://github.com/d3athrow/vgstation13/pull/6625 for more details.

code/datums/helper_datums/construction_datum.dm

@@ -61,7 +61,8 @@
 		else if(istype(used_atom, /obj/item/stack/cable_coil))
 			var/obj/item/stack/cable_coil/C = used_atom
 			if(C.amount<4)
-				user << ("There's not enough cable to finish the task.")
+				to_chat(user, ("There's not enough cable to finish the task."))
+
 				return 0
 			else
 				C.use(4)
@@ -69,7 +70,8 @@
 		else if(istype(used_atom, /obj/item/stack))
 			var/obj/item/stack/S = used_atom
 			if(S.amount < 5)
-				user << ("There's not enough material in this stack.")
+				to_chat(user, ("There's not enough material in this stack."))
+
 				return 0
 			else
 				S.use(5)
@@ -111,24 +113,28 @@
 			if(istype(used_atom,/obj/item/stack))
 				var/obj/item/stack/stack=used_atom
 				if(stack.amount < amount)
-					user << "\red You don't have enough [stack]! You need at least [amount]."
+					to_chat(user, "\red You don't have enough [stack]! You need at least [amount].")
+
 					return 0
 				stack.use(amount)
 			// CABLES
 			if(istype(used_atom,/obj/item/stack/cable_coil))
 				var/obj/item/stack/cable_coil/coil=used_atom
 				if(coil.amount < amount)
-					user << "\red You don't have enough cable! You need at least [amount] coils."
+					to_chat(user, "\red You don't have enough cable! You need at least [amount] coils.")
+
 					return 0
 				coil.use(amount)
 			// WELDER
 			if(istype(used_atom,/obj/item/weapon/weldingtool))
 				var/obj/item/weapon/weldingtool/welder=used_atom
 				if(!welder.isOn())
-					user << "\blue You tap the [src] with your unlit welder.  [pick("Ding","Dong")]."
+					to_chat(user, "\blue You tap the [src] with your unlit welder.  [pick("Ding","Dong")].")
+
 					return 0
 				if(!welder.remove_fuel(amount,user))
-					user << "\red You don't have enough fuel!"
+					to_chat(user, "\red You don't have enough fuel!")
+
 					return 0
 		return 1
 

code/datums/helper_datums/events.dm

@@ -31,7 +31,8 @@
 	//  Arguments: event_type as text, any number of additional arguments to pass to event handler
 	//  Returns: null
 	proc/fireEvent()
-		//world << "Events in [args[1]] called"
+//		to_chat(world, "Events in [args[1]] called")
+
 		var/list/event = listgetindex(events,args[1])
 		if(istype(event))
 			spawn(-1)
@@ -60,7 +61,8 @@
 		return ..()
 
 	proc/Fire()
-		//world << "Event fired"
+//		to_chat(world, "Event fired")
+
 		if(listener)
 			call(listener,proc_name)(arglist(args))
 			return 1

code/datums/helper_datums/global_iterator.dm

@@ -139,7 +139,8 @@ Data storage vars:
 			arg_list = arguments
 			return 1
 		else
-//			world << "\red Invalid arguments supplied for [src.type], ref = \ref[src]"
+//			to_chat(world, "\red Invalid arguments supplied for [src.type], ref = \ref[src]")
+
 			return 0
 
 	proc/toggle_null_checks()

code/datums/helper_datums/teleport.dm

@@ -166,5 +166,6 @@
 		precision = max(rand(1,100)*bagholding.len,100)
 		if(istype(teleatom, /mob/living))
 			var/mob/living/MM = teleatom
-			MM << "<span class='warning'>The bluespace interface on your bag of holding interferes with the teleport!</span>"
+			to_chat(MM, "<span class='warning'>The bluespace interface on your bag of holding interferes with the teleport!</span>")
+
 	return 1