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/Gateway/SharedGatewayGeneratorSystem.cs

@@ -0,0 +1,12 @@
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Gateway;
+
+/// <summary>
+/// Sent from client to server upon taking a gateway destination.
+/// </summary>
+[Serializable, NetSerializable]
+public sealed class GatewayDestinationMessage : EntityEventArgs
+{
+    public int Index;
+}