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/Alerts/ClientAlertsSystem.cs

@@ -9,7 +9,7 @@ using Robust.Shared.Prototypes;
 namespace Content.Client.Alerts;
 
 [UsedImplicitly]
-internal sealed class ClientAlertsSystem : AlertsSystem
+public sealed class ClientAlertsSystem : AlertsSystem
 {
     public AlertOrderPrototype? AlertOrder { get; set; }