Various UI warnings cleanup (#36169)

* Various UI warnings cleanup

* Revert unnecessary change

* Redoing SpriteSystem as it's non-injectable

* Missed one

* Better entity instantiation

* General cleanup of warnings changes

* Wrong class name!

Content.Client/Decals/UI/DecalPlacerWindow.xaml.cs

@@ -2,6 +2,7 @@ using System.Linq;
 using Content.Client.Stylesheets;
 using Content.Shared.Decals;
 using Robust.Client.AutoGenerated;
+using Robust.Client.GameObjects;
 using Robust.Client.Graphics;
 using Robust.Client.UserInterface.Controls;
 using Robust.Client.UserInterface.CustomControls;
@@ -19,6 +20,7 @@ public sealed partial class DecalPlacerWindow : DefaultWindow
     [Dependency] private readonly IEntityManager _e = default!;
 
     private readonly DecalPlacementSystem _decalPlacementSystem;
+    private readonly SpriteSystem _sprite;
 
     public FloatSpinBox RotationSpinBox;
 
@@ -41,6 +43,7 @@ public sealed partial class DecalPlacerWindow : DefaultWindow
         IoCManager.InjectDependencies(this);
 
         _decalPlacementSystem = _e.System<DecalPlacementSystem>();
+        _sprite = _e.System<SpriteSystem>();
 
         // This needs to be done in C# so we can have custom stuff passed in the constructor
         // and thus have a proper step size
@@ -204,7 +207,7 @@ public sealed partial class DecalPlacerWindow : DefaultWindow
         foreach (var decalPrototype in prototypes)
         {
             if (decalPrototype.ShowMenu)
-                _decals.Add(decalPrototype.ID, decalPrototype.Sprite.Frame0());
+                _decals.Add(decalPrototype.ID, _sprite.Frame0(decalPrototype.Sprite));
         }
 
         RefreshList();