Revert "Remove some BUI boilerplate" (#30214)

Revert "Remove some BUI boilerplate (#28399)"

This reverts commit cbf329a82d.

Content.Client/Construction/UI/FlatpackCreatorBoundUserInterface.cs

@@ -1,6 +1,5 @@
 using Content.Shared.Construction.Components;
 using JetBrains.Annotations;
-using Robust.Client.UserInterface;
 
 namespace Content.Client.Construction.UI
 {
@@ -18,8 +17,8 @@ namespace Content.Client.Construction.UI
         {
             base.Open();
 
-            _menu = this.CreateWindow<FlatpackCreatorMenu>();
-            _menu.SetEntity(Owner);
+            _menu = new FlatpackCreatorMenu(Owner);
+            _menu.OnClose += Close;
 
             _menu.PackButtonPressed += () =>
             {
@@ -28,5 +27,14 @@ namespace Content.Client.Construction.UI
 
             _menu.OpenCentered();
         }
+
+        protected override void Dispose(bool disposing)
+        {
+            base.Dispose(disposing);
+            if (!disposing)
+                return;
+
+            _menu?.Dispose();
+        }
     }
 }