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/Hands/Systems/HandsSystem.cs

@@ -1,6 +1,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Content.Client.Animations;
+using Content.Client.Hands.UI;
 using Content.Client.HUD;
 using Content.Shared.Hands;
 using Content.Shared.Hands.Components;
@@ -14,7 +15,7 @@ using Robust.Shared.GameStates;
 using Robust.Shared.Map;
 using Robust.Shared.Timing;
 
-namespace Content.Client.Hands
+namespace Content.Client.Hands.Systems
 {
     [UsedImplicitly]
     public sealed class HandsSystem : SharedHandsSystem