genericize ui fragments (#12810)

Content.Client/UserInterface/Fragments/UIFragment.cs

@@ -0,0 +1,25 @@
+using Robust.Client.GameObjects;
+using Robust.Client.UserInterface;
+
+namespace Content.Client.UserInterface.Fragments;
+
+/// <summary>
+/// Specific ui fragments need to inherit this class. The subclass is then used in yaml to tell a main ui to use it as a ui fragment.
+/// </summary>
+/// <example>
+/// This is an example from the yaml definition from the notekeeper ui
+/// <code>
+/// - type: CartridgeUi
+///     ui: !type:NotekeeperUi
+/// </code>
+/// </example>
+[ImplicitDataDefinitionForInheritors]
+public abstract class UIFragment
+{
+    public abstract Control GetUIFragmentRoot();
+
+    public abstract void Setup(BoundUserInterface userInterface);
+
+    public abstract void UpdateState(BoundUserInterfaceState state);
+
+}