…ocess icon (microsoft#42316)

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## Summary of the Pull Request

This is a PR for issue **microsoft#42260**.
It targets **CmdPal’s WindowWalker** and changes the icon retrieval to
use **SendMessage** to obtain the window’s actual icon, instead of using
the **process icon**.

To support this, I added a new configuration option.

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## PR Checklist

- [ ] Closes: microsoft#42260
- [ ] **Communication:** @jiripolasek 
- [ ] **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
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and link it here: #xxx

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## Detailed Description of the Pull Request / Additional comments


Actully, The `ThumbnailHelper` already contains code that converts an
`IntPtr` `hIcon` into an `IRandomAccessStream`, as shown below:

```
 private static MemoryStream GetMemoryStreamFromIcon(IntPtr hIcon)
 {
     var memoryStream = new MemoryStream();

     // Ensure disposing the icon before freeing the handle
     using (var icon = Icon.FromHandle(hIcon))
     {
         icon.ToBitmap().Save(memoryStream, System.Drawing.Imaging.ImageFormat.Png);
     }

     // Clean up the unmanaged handle without risking a use-after-free.
     NativeMethods.DestroyIcon(hIcon);

     memoryStream.Position = 0;
     return memoryStream;
 }

 private static async Task<IRandomAccessStream?> FromHIconToStream(IntPtr hIcon)
 {
     var stream = new InMemoryRandomAccessStream();

     using var memoryStream = GetMemoryStreamFromIcon(hIcon); // this will DestroyIcon hIcon
     using var outputStream = stream.GetOutputStreamAt(0);
     using var dataWriter = new DataWriter(outputStream);

     dataWriter.WriteBytes(memoryStream.ToArray());
     await dataWriter.StoreAsync();
     await dataWriter.FlushAsync();

     return stream;
 }
```

Without modifying (or using) this code, I implemented the almost same
logic directly in `SwitchToWindowCommand` (calling the async code with
`Wait` to block synchronously). The reasons are:

1. I wanted to limit changes to the **WindowWalker** project area. I
don’t expect other extensions to need this behavior.
2. Because this is resource-related work, exposing a public helper that
pulls memory from an `hIcon` pointer seems risky—especially in a class
like `ThumbnailHelper`.

Therefore, I implemented behavior that is nearly identical to the
snippet above.

I did use `using`/`Dispose` where appropriate, but the
`InMemoryRandomAccessStream` created for `IconInfo.FromStream` appears
to use internal referencing; disposing it would be incorrect. For that
reason I didn’t wrap it in a `using`. I’m not entirely sure whether GC
will handle this cleanly.

However, based on the implementation of `FromStream` itself and its
usage elsewhere (e.g., in `ThumbnailHelper`), this seems to be the
correct usage pattern, though I’m not entirely sure.

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---------

Co-authored-by: Jiří Polášek <[email protected]>