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

@@ -0,0 +1,21 @@
+
+<controls:FancyWindow xmlns="https://spacestation14.io"
+                      xmlns:controls="clr-namespace:Content.Client.UserInterface.Controls"
+                      MouseFilter="Stop"
+                      MinWidth="200" MinHeight="150">
+    <PanelContainer StyleClasses="AngleRect" />
+
+    <BoxContainer Orientation="Vertical">
+        <Control>
+            <PanelContainer StyleClasses="WindowHeadingBackground" />
+            <BoxContainer Margin="4 2 8 0" Orientation="Horizontal">
+                <Label Name="WindowTitle"
+                       HorizontalExpand="True" VAlign="Center" StyleClasses="FancyWindowTitle" />
+                <TextureButton Name="CloseButton" StyleClasses="windowCloseButton"
+                               VerticalAlignment="Center" />
+            </BoxContainer>
+        </Control>
+        <PanelContainer StyleClasses="LowDivider" />
+        <Control Access="Public" Name="ContentsContainer" Margin="0 2" RectClipContent="True" VerticalExpand="true" />
+    </BoxContainer>
+</controls:FancyWindow>

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

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+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;
+        }
+    }
+}

Content.Client/UserInterface/Controls/HighDivider.cs

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+using Content.Client.Stylesheets;
+using Robust.Client.UserInterface;
+using Robust.Client.UserInterface.Controls;
+
+namespace Content.Client.UserInterface.Controls
+{
+    public sealed class HighDivider : Control
+    {
+        public HighDivider()
+        {
+            Children.Add(new PanelContainer {StyleClasses = {StyleBase.ClassHighDivider}});
+        }
+    }
+}