Show if items can be placed in a slot when hovering (#1480)

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>

Content.Client/UserInterface/IItemSlotManager.cs

@@ -9,5 +9,6 @@ namespace Content.Client.UserInterface
         bool OnButtonPressed(GUIBoundKeyEventArgs args, IEntity item);
         void UpdateCooldown(ItemSlotButton cooldownTexture, IEntity entity);
         bool SetItemSlot(ItemSlotButton button, IEntity entity);
+        void HoverInSlot(ItemSlotButton button, IEntity entity, bool fits);
     }
 }