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/Changelog/ChangelogWindow.xaml

@@ -1,6 +1,6 @@
 <changelog:ChangelogWindow xmlns="https://spacestation14.io"
                            xmlns:changelog="clr-namespace:Content.Client.Changelog"
-                           xmlns:ui="clr-namespace:Content.Client.HUD.UI"
+                           xmlns:controls="clr-namespace:Content.Client.UserInterface.Controls"
                            MinSize="500 400" MouseFilter="Stop">
     <PanelContainer StyleClasses="AngleRect" />
     <BoxContainer Orientation="Vertical">
@@ -10,7 +10,7 @@
             <TextureButton Margin="0 0 8 0" Name="CloseButton" StyleClasses="windowCloseButton"
                            VerticalAlignment="Center" />
         </BoxContainer>
-        <ui:HighDivider />
+        <controls:HighDivider />
 
         <ScrollContainer VerticalExpand="True" HScrollEnabled="False">
             <BoxContainer Orientation="Vertical" Name="ChangelogBody" />