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/Mech/Ui/MechMenu.xaml.cs

@@ -16,14 +16,15 @@ public sealed partial class MechMenu : FancyWindow
 
     public event Action<EntityUid>? OnRemoveButtonPressed;
 
-    public MechMenu(EntityUid mech)
+    public MechMenu()
     {
         RobustXamlLoader.Load(this);
         IoCManager.InjectDependencies(this);
+    }
 
-        _mech = mech;
-
-        MechView.SetEntity(mech);
+    public void SetEntity(EntityUid uid)
+    {
+        MechView.SetEntity(uid);
     }
 
     public void UpdateMechStats()