Gateway destinations (#21040)

* Gateway generation

* Gateway stuff

* gatewehs

* mercenaries

* play area

* Range fixes and tweaks

* weh

* Gateway UI polish

* Lots of fixes

* Knock some items off

* Fix dungeon spawning

Realistically we should probably be using a salvage job.

* wahwah

* wehvs

* expression

* weh

* eee

* a

* a

* WEH

* frfr

* Gatwey

* Fix gateway windows

* Fix gateway windows

* a

* a

* Better layer masking

* a

* a

* Noise fixes

* a

* Fix fractal calculations

* a

* More fixes

* Fixes

* Add layers back in

* Fixes

* namespaces and ftl

* Other TODO

* Fix distance

* Cleanup

* Fix test

Content.Shared/Teleportation/Systems/LinkedEntitySystem.cs

@@ -54,13 +54,29 @@ public sealed class LinkedEntitySystem : EntitySystem
         _appearance.SetData(first, LinkedEntityVisuals.HasAnyLinks, true);
         _appearance.SetData(second, LinkedEntityVisuals.HasAnyLinks, true);
 
-        Dirty(firstLink);
-        Dirty(secondLink);
+        Dirty(first, firstLink);
+        Dirty(second, secondLink);
 
         return firstLink.LinkedEntities.Add(second)
             && secondLink.LinkedEntities.Add(first);
     }
 
+    /// <summary>
+    /// Does a one-way link from source to target.
+    /// </summary>
+    /// <param name="deleteOnEmptyLinks">Whether both entities should now delete once their links are removed</param>
+    public bool OneWayLink(EntityUid source, EntityUid target, bool deleteOnEmptyLinks=false)
+    {
+        var firstLink = EnsureComp<LinkedEntityComponent>(source);
+        firstLink.DeleteOnEmptyLinks = deleteOnEmptyLinks;
+
+        _appearance.SetData(source, LinkedEntityVisuals.HasAnyLinks, true);
+
+        Dirty(source, firstLink);
+
+        return firstLink.LinkedEntities.Add(target);
+    }
+
     /// <summary>
     ///     Unlinks two entities. Deletes either entity if <see cref="LinkedEntityComponent.DeleteOnEmptyLinks"/>
     ///     was true and its links are now empty. Symmetrical, so order doesn't matter.