Remove some BUI boilerplate (#28399)

* Remove some BUI boilerplate

- The disposals overrides got removed due to the helper method handling it.
- Replace window creation with CreateWindow helper.
- Fixed some stinky code which would cause exceptions.

* More

* moar

* weh

* done

* More BUIs

* More updates

* weh

* moar

* look who it is

* weh

* merge

* weh

* fixes

Content.Client/Gateway/UI/GatewayBoundUserInterface.cs

@@ -1,6 +1,7 @@
 using Content.Shared.Gateway;
 using JetBrains.Annotations;
 using Robust.Client.GameObjects;
+using Robust.Client.UserInterface;
 
 namespace Content.Client.Gateway.UI;
 
@@ -17,24 +18,13 @@ public sealed class GatewayBoundUserInterface : BoundUserInterface
     {
         base.Open();
 
-        _window = new GatewayWindow(EntMan.GetNetEntity(Owner));
+        _window = this.CreateWindow<GatewayWindow>();
+        _window.SetEntity(EntMan.GetNetEntity(Owner));
 
         _window.OpenPortal += destination =>
         {
             SendMessage(new GatewayOpenPortalMessage(destination));
         };
-        _window.OnClose += Close;
-        _window?.OpenCentered();
-    }
-
-    protected override void Dispose(bool disposing)
-    {
-        base.Dispose(disposing);
-        if (disposing)
-        {
-            _window?.Dispose();
-            _window = null;
-        }
     }
 
     protected override void UpdateState(BoundUserInterfaceState state)