cleanup changeling namespaces and prototypes (#39794)

Content.Shared/Changeling/Systems/ChangelingTransformSystem.UI.cs

@@ -0,0 +1,33 @@
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Changeling.Systems;
+
+/// <summary>
+/// Send when a player selects an intentity to transform into in the radial menu.
+/// </summary>
+[Serializable, NetSerializable]
+public sealed class ChangelingTransformIdentitySelectMessage(NetEntity targetIdentity) : BoundUserInterfaceMessage
+{
+    /// <summary>
+    /// The uid of the cloned identity.
+    /// </summary>
+    public readonly NetEntity TargetIdentity = targetIdentity;
+}
+
+// TODO: Replace with component states.
+// We are already networking the ChangelingIdentityComponent, which contains all this information,
+// so we can just read it from them from the component and update the UI in an AfterAuotHandleState subscription.
+[Serializable, NetSerializable]
+public sealed class ChangelingTransformBoundUserInterfaceState(List<NetEntity> identities) : BoundUserInterfaceState
+{
+    /// <summary>
+    /// The uids of the cloned identities.
+    /// </summary>
+    public readonly List<NetEntity> Identites = identities;
+}
+
+[Serializable, NetSerializable]
+public enum TransformUI : byte
+{
+    Key,
+}