[Settings] Optimizing and cleaning up code (#44721)

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fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request

- Removing dead experiments code
- Refactoring and simplifying OOBE/SCOOBE windowing code
- Removing dead assets
- Optimizing CmdPal assets to lower res shaving off a few MBs
- Scrolling works better on the What's new page
- Should be merged after: #44638

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## PR Checklist

- [X] Closes: #44958
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

---------

Co-authored-by: Gordon Lam (SH) <yeelam@microsoft.com>

src/settings-ui/Settings.UI/SettingsXAML/MainWindow.xaml.cs

@@ -12,6 +12,7 @@ using Microsoft.PowerToys.Settings.UI.Library.Helpers;
 using Microsoft.PowerToys.Settings.UI.Views;
 using Microsoft.PowerToys.Telemetry;
 using Microsoft.UI;
+using Microsoft.UI.Dispatching;
 using Microsoft.UI.Windowing;
 using Microsoft.UI.Xaml;
 using Windows.Data.Json;
@@ -75,7 +76,7 @@ namespace Microsoft.PowerToys.Settings.UI
             // open main window
             ShellPage.SetOpenMainWindowCallback(type =>
             {
-                DispatcherQueue.TryEnqueue(Microsoft.UI.Dispatching.DispatcherQueuePriority.Normal, () =>
+                DispatcherQueue.TryEnqueue(DispatcherQueuePriority.Normal, () =>
                      App.OpenSettingsWindow(type));
             });
 
@@ -106,30 +107,8 @@ namespace Microsoft.PowerToys.Settings.UI
                 return needToUpdate;
             });
 
-            // open oobe
-            ShellPage.SetOpenOobeCallback(() =>
-            {
-                if (App.GetOobeWindow() == null)
-                {
-                    App.SetOobeWindow(new OobeWindow(OOBE.Enums.PowerToysModules.Overview));
-                }
-
-                App.GetOobeWindow().Activate();
-            });
-
-            // open whats new window
-            ShellPage.SetOpenWhatIsNewCallback(() =>
-            {
-                if (App.GetScoobeWindow() == null)
-                {
-                    App.SetScoobeWindow(new ScoobeWindow());
-                }
-
-                App.GetScoobeWindow().Activate();
-            });
-
             this.InitializeComponent();
-            SetAppTitleBar();
+            SetTitleBar();
 
             // receive IPC Message
             App.IPCMessageReceivedCallback = (string msg) =>
@@ -156,21 +135,22 @@ namespace Microsoft.PowerToys.Settings.UI
             PowerToysTelemetry.Log.WriteEvent(new SettingsBootEvent() { BootTimeMs = bootTime.ElapsedMilliseconds });
         }
 
-        private void SetAppTitleBar()
+        private void SetTitleBar()
         {
             // We need to assign the window here so it can configure the custom title bar area correctly.
             shellPage.TitleBar.Window = this;
+            this.ExtendsContentIntoTitleBar = true;
             WindowHelpers.ForceTopBorder1PixelInsetOnWindows10(WindowNative.GetWindowHandle(this));
         }
 
-        public void NavigateToSection(System.Type type)
+        public void NavigateToSection(Type type)
         {
             ShellPage.Navigate(type);
         }
 
         public void CloseHiddenWindow()
         {
-            var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(this);
+            var hWnd = WindowNative.GetWindowHandle(this);
             if (!NativeMethods.IsWindowVisible(hWnd))
             {
                 Close();
@@ -179,10 +159,10 @@ namespace Microsoft.PowerToys.Settings.UI
 
         private void Window_Closed(object sender, WindowEventArgs args)
         {
-            var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(this);
+            var hWnd = WindowNative.GetWindowHandle(this);
             WindowHelper.SerializePlacement(hWnd);
 
-            if (App.GetOobeWindow() == null && App.GetScoobeWindow() == null)
+            if (!App.IsOobeOrScoobeOpen())
             {
                 App.ClearSettingsWindow();
             }
@@ -198,10 +178,7 @@ namespace Microsoft.PowerToys.Settings.UI
         private void Window_Activated_SetIcon(object sender, WindowActivatedEventArgs args)
         {
             // Set window icon
-            var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(this);
-            WindowId windowId = Win32Interop.GetWindowIdFromWindow(hWnd);
-            AppWindow appWindow = AppWindow.GetFromWindowId(windowId);
-            appWindow.SetIcon("Assets\\Settings\\icon.ico");
+            this.SetIcon("Assets\\Settings\\icon.ico");
         }
 
         private void Window_Activated(object sender, WindowActivatedEventArgs args)
@@ -209,7 +186,7 @@ namespace Microsoft.PowerToys.Settings.UI
             if (args.WindowActivationState != WindowActivationState.Deactivated)
             {
                 this.Activated -= Window_Activated;
-                var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(this);
+                var hWnd = WindowNative.GetWindowHandle(this);
                 var placement = WindowHelper.DeserializePlacementOrDefault(hWnd);
                 NativeMethods.SetWindowPlacement(hWnd, ref placement);
             }