CmdPal: Fixes and improve main window positioning (#45585)

## Summary of the Pull Request

This PR improves main window positioning:

- Fixes cases where an invalid window size or position was saved.  
- `UpdateWindowPositionInMemory` failed to capture correct values when
the window was minimized or maximized (for example, a minimized window
reports coordinates like `(-32000, -32000)`).
- Improves repositioning logic to use relative anchors (corners and
center). When switching displays, the window should reappear in the
expected position. This also reduces cases that trigger the failsafe
recentering.
- Fixes the dragging rectangle size after switching DPIs - the rectangle
was not adapting, so it when switching from 100 % to 200 % it covered
only left half of the window and had teeny-tiny height.
- Suppresses system DPI handling during summon to prevent double
scaling.
- Makes `WindowPosition` class immutable.
- Adds light-weight failsafe preventing overwriting position with
invalid data.
- Hotfixes a min/max state conflict with the WinUIEx window manager.

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## PR Checklist

- [x] Closes: #45576
<!-- - [ ] 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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## Detailed Description of the Pull Request / Additional comments

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## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/WindowPosition.cs

@@ -11,37 +11,42 @@ public sealed class WindowPosition
     /// <summary>
     /// Gets or sets left position in device pixels.
     /// </summary>
-    public int X { get; set; }
+    public int X { get; init; }
 
     /// <summary>
     /// Gets or sets top position in device pixels.
     /// </summary>
-    public int Y { get; set; }
+    public int Y { get; init; }
 
     /// <summary>
     /// Gets or sets width in device pixels.
     /// </summary>
-    public int Width { get; set; }
+    public int Width { get; init; }
 
     /// <summary>
     /// Gets or sets height in device pixels.
     /// </summary>
-    public int Height { get; set; }
+    public int Height { get; init; }
 
     /// <summary>
     /// Gets or sets width of the screen in device pixels where the window is located.
     /// </summary>
-    public int ScreenWidth { get; set; }
+    public int ScreenWidth { get; init; }
 
     /// <summary>
     /// Gets or sets height of the screen in device pixels where the window is located.
     /// </summary>
-    public int ScreenHeight { get; set; }
+    public int ScreenHeight { get; init; }
 
     /// <summary>
     /// Gets or sets DPI (dots per inch) of the display where the window is located.
     /// </summary>
-    public int Dpi { get; set; }
+    public int Dpi { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating whether the width and height of the window are valid (greater than 0).
+    /// </summary>
+    public bool IsSizeValid => Width > 0 && Height > 0;
 
     /// <summary>
     /// Converts the window position properties to a <see cref="RectInt32"/> structure representing the physical window rectangle.