CmdPal: Did someone say grid pages? (#40832)

Closes #38269

Still working on this one, but essentially allows a list page to become
a grid page by specifying a `GridProperties` property like so:

```C#
public AllAppsPage()
{
    PlaceholderText = Resources.search_installed_apps_placeholder;
    GridProperties = new MediumGridLayout();
}
```

> This is a very early version and very subject to change. Much to
clean, but feedback & suggestions are welcome.

## Current preview

### SmallGridLayout

<img width="998" height="607" alt="image"
src="https://github.com/user-attachments/assets/ebdf11fd-6c86-4fc3-bf49-bcbb5d32caa4"
/>


### MediumGridLayout

<img width="976" height="586" alt="image"
src="https://github.com/user-attachments/assets/82daa2e9-548e-4864-8885-1c486ca9f891"
/>

### GalleryGridLayout

<img width="988" height="600" alt="image"
src="https://github.com/user-attachments/assets/23ca486a-35c7-467a-b200-4f6ee5f4a95c"
/>

---------

Co-authored-by: Mike Griese <migrie@microsoft.com>

src/modules/cmdpal/ext/SamplePagesExtension/SamplesListPage.cs

@@ -33,6 +33,11 @@ public partial class SamplesListPage : ListPage
             Title = "Dynamic List Page Command",
             Subtitle = "Changes the list of items in response to the typed query",
         },
+        new ListItem(new SampleGalleryListPage())
+        {
+            Title = "Gallery List Page Command",
+            Subtitle = "Displays items as a gallery",
+        },
         new ListItem(new OnLoadPage())
         {
             Title = "Demo of OnLoad/OnUnload",