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>

.github/actions/spell-check/expect.txt

@@ -1451,7 +1451,6 @@ rstringalnum
 rstringalpha
 rstringdigit
 rtb
-RTB
 RTLREADING
 rtm
 runas