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/Atmos/UI/GasMixerBoundUserInteface.cs

@@ -2,7 +2,7 @@ using Content.Shared.Atmos;
 using Content.Shared.Atmos.Piping.Trinary.Components;
 using Content.Shared.Localizations;
 using JetBrains.Annotations;
-using Robust.Client.GameObjects;
+using Robust.Client.UserInterface;
 
 namespace Content.Client.Atmos.UI
 {
@@ -26,14 +26,7 @@ namespace Content.Client.Atmos.UI
         {
             base.Open();
 
-            _window = new GasMixerWindow();
-
-            if (State != null)
-                UpdateState(State);
-
-            _window.OpenCentered();
-
-            _window.OnClose += Close;
+            _window = this.CreateWindow<GasMixerWindow>();
 
             _window.ToggleStatusButtonPressed += OnToggleStatusButtonPressed;
             _window.MixerOutputPressureChanged += OnMixerOutputPressurePressed;
@@ -83,12 +76,5 @@ namespace Content.Client.Atmos.UI
             _window.SetOutputPressure(cast.OutputPressure);
             _window.SetNodePercentages(cast.NodeOne);
         }
-
-        protected override void Dispose(bool disposing)
-        {
-            base.Dispose(disposing);
-            if (!disposing) return;
-            _window?.Dispose();
-        }
     }
 }