feat: added mouse positioner behaviour

Shared/Behaviours/MousePositionerBehaviour.cs

@@ -0,0 +1,21 @@
+using Microsoft.Xna.Framework.Input;
+
+using Engine.Core;
+using Engine.Integration.MonoGame;
+
+namespace MyUniverse.Shared.Behaviours;
+
+public class MousePositionerBehaviour : Behaviour2D, IUpdate, IFirstFrameUpdate
+{
+    private ICamera2D camera = null!;
+
+    public void FirstActiveFrame()
+    {
+        camera = Universe.FindRequiredBehaviour<ICamera2D>();
+    }
+
+    public void Update()
+    {
+        Transform.Position = camera.ScreenToWorldPosition(Mouse.GetState().Position.ToVector2D());
+    }
+}