Refactor UserInterface properties to use a helper (#1896)

Content.Server/Utility/UserInterfaceHelpers.cs

@@ -0,0 +1,14 @@
+#nullable enable
+using Robust.Server.GameObjects.Components.UserInterface;
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Server.Utility
+{
+    public static class UserInterfaceHelpers
+    {
+        public static BoundUserInterface? GetUIOrNull(this IEntity entity, object uiKey)
+        {
+            return entity.GetComponentOrNull<ServerUserInterfaceComponent>()?.GetBoundUserInterfaceOrNull(uiKey);
+        }
+    }
+}