Overmap exoplanet generation, ported from Bay. (#12362)

code/modules/random_map/random_map.dm

@@ -25,6 +25,8 @@ var/global/list/map_count = list()
 	var/target_turf_type
 	var/spawn_roof = FALSE //Set to TRUE if a roof should be spawned based.
 
+	var/area/use_area // If set, turfs will be put in this area. If set to type, new instance will be spawned for the map
+
 	// Storage for the final iteration of the map.
 	var/list/map = list()           // Actual map.
 	var/tmp/map_len = 0
@@ -33,7 +35,7 @@ var/global/list/map_count = list()
 	// Test to see if rand_seed() can be used reliably.
 	var/priority_process
 
-/datum/random_map/New(var/seed, var/tx, var/ty, var/tz, var/tlx, var/tly, var/do_not_apply, var/do_not_announce)
+/datum/random_map/New(var/seed, var/tx, var/ty, var/tz, var/tlx, var/tly, var/do_not_apply, var/do_not_announce, var/never_be_priority = 0, var/used_area)
 
 	// Store this for debugging.
 	if(!map_count[descriptor])
@@ -48,6 +50,12 @@ var/global/list/map_count = list()
 	if(tlx) limit_x = tlx
 	if(tly) limit_y = tly
 
+	if(used_area)
+		if(ispath(used_area))
+			use_area = new(used_area)
+		else
+			use_area = used_area
+
 	if(do_not_apply)
 		auto_apply = null
 
@@ -61,7 +69,7 @@ var/global/list/map_count = list()
 	// Testing needed to see how reliable this is (asynchronous calls, called during worldgen), DM ref is not optimistic
 	if(seed)
 		rand_seed(seed)
-		priority_process = 1
+		priority_process = !never_be_priority
 
 	for(var/i = 0;i<max_attempts;i++)
 		if(generate())
@@ -183,6 +191,8 @@ var/global/list/map_count = list()
 	if(spawn_roof)
 		T.spawn_roof()
 	get_additional_spawns(map[tmp_cell],T,get_spawn_dir(x, y))
+	if(use_area)
+		ChangeArea(T, use_area)
 	return T
 
 /datum/random_map/proc/get_spawn_dir()