Move/Rename stuff (#11209)

-     Change namespace, and folder of FancyWindow to Content.Client.UserInterface.Controls
-     Change xaml reference from ui to controls in some places
-     Change ClientAlertsSystem from internal to public
-     Change namespace, and folder of HighDivider to Content.Client.UserInterface.Controls

Content.Client/UserInterface/Controls/FancyWindow.xaml.cs

@@ -0,0 +1,31 @@
+using Robust.Client.AutoGenerated;
+using Robust.Client.UserInterface.CustomControls;
+using Robust.Client.UserInterface.XAML;
+using Robust.Shared.Maths;
+
+namespace Content.Client.UserInterface.Controls
+{
+    [GenerateTypedNameReferences]
+    [Virtual]
+    public partial class FancyWindow : BaseWindow
+    {
+        public FancyWindow()
+        {
+            RobustXamlLoader.Load(this);
+
+            CloseButton.OnPressed += _ => Close();
+            XamlChildren = ContentsContainer.Children;
+        }
+
+        public string? Title
+        {
+            get => WindowTitle.Text;
+            set => WindowTitle.Text = value;
+        }
+
+        protected override DragMode GetDragModeFor(Vector2 relativeMousePos)
+        {
+            return DragMode.Move;
+        }
+    }
+}