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/Construction/UI/FlatpackCreatorMenu.xaml.cs

@@ -24,7 +24,7 @@ public sealed partial class FlatpackCreatorMenu : FancyWindow
     private readonly FlatpackSystem _flatpack;
     private readonly MaterialStorageSystem _materialStorage;
 
-    private readonly EntityUid _owner;
+    private EntityUid _owner;
 
     [ValidatePrototypeId<EntityPrototype>]
     public const string NoBoardEffectId = "FlatpackerNoBoardEffect";
@@ -33,7 +33,7 @@ public sealed partial class FlatpackCreatorMenu : FancyWindow
 
     public event Action? PackButtonPressed;
 
-    public FlatpackCreatorMenu(EntityUid uid)
+    public FlatpackCreatorMenu()
     {
         RobustXamlLoader.Load(this);
         IoCManager.InjectDependencies(this);
@@ -42,14 +42,17 @@ public sealed partial class FlatpackCreatorMenu : FancyWindow
         _flatpack = _entityManager.System<FlatpackSystem>();
         _materialStorage = _entityManager.System<MaterialStorageSystem>();
 
-        _owner = uid;
-
         PackButton.OnPressed += _ => PackButtonPressed?.Invoke();
 
-        MaterialStorageControl.SetOwner(uid);
         InsertLabel.SetMarkup(Loc.GetString("flatpacker-ui-insert-board"));
     }
 
+    public void SetEntity(EntityUid uid)
+    {
+        _owner = uid;
+        MaterialStorageControl.SetOwner(uid);
+    }
+
     protected override void FrameUpdate(FrameEventArgs args)
     {
         base.FrameUpdate(args);