CmdPal: Filters for DynamicListPage? Yes, please. (#40783)

Closes: #40382

## To-do list

- [x] Add support for "single-select" filters to DynamicListPage
- [x] Filters can contain icons
- [x] Filter list can contain separators
- [x] Update Windows Services built-in extension to support filtering by
all, started, stopped, and pending services
- [x] Update SampleExtension dynamic list sample to filter.

## Example of filters in use

```C#
internal sealed partial class ServicesListPage : DynamicListPage
{
    public ServicesListPage()
    {
        Icon = Icons.ServicesIcon;
        Name = "Windows Services";

        var filters = new ServiceFilters();
        filters.PropChanged += Filters_PropChanged;
        Filters = filters;
    }

    private void Filters_PropChanged(object sender, IPropChangedEventArgs args) => RaiseItemsChanged();

    public override void UpdateSearchText(string oldSearch, string newSearch) => RaiseItemsChanged();

    public override IListItem[] GetItems()
    {
       // ServiceHelper.Search knows how to filter based on the CurrentFilterIds provided
        var items = ServiceHelper.Search(SearchText, Filters.CurrentFilterIds).ToArray();

        return items;
    }
}

public partial class ServiceFilters : Filters
{
    public ServiceFilters()
    {
        // This would be a default selection. Not providing this will cause the filter
        // control to display the "Filter" placeholder text.
        CurrentFilterIds = ["all"];
    }

    public override IFilterItem[] GetFilters()
    {
        return [
            new Filter() { Id = "all", Name = "All Services" },
            new Separator(),
            new Filter() { Id = "running", Name = "Running", Icon = Icons.GreenCircleIcon },
            new Filter() { Id = "stopped", Name = "Stopped", Icon = Icons.RedCircleIcon },
            new Filter() { Id = "paused", Name = "Paused", Icon = Icons.PauseIcon },
        ];
    }
}
```

## Current example of behavior


https://github.com/user-attachments/assets/2e325763-ad3a-4445-bbe2-a840df08d0b3

---------

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

src/modules/cmdpal/Microsoft.CmdPal.UI/Controls/SearchBar.xaml.cs

@@ -62,7 +62,7 @@ public sealed partial class SearchBar : UserControl,
         {
             // TODO: In some cases we probably want commands to clear a filter
             // somewhere in the process, so we need to figure out when that is.
-            @this.FilterBox.Text = page.Filter;
+            @this.FilterBox.Text = page.SearchTextBox;
             @this.FilterBox.Select(@this.FilterBox.Text.Length, 0);
 
             page.PropertyChanged += @this.Page_PropertyChanged;
@@ -87,7 +87,7 @@ public sealed partial class SearchBar : UserControl,
 
             if (CurrentPageViewModel is not null)
             {
-                CurrentPageViewModel.Filter = string.Empty;
+                CurrentPageViewModel.SearchTextBox = string.Empty;
             }
         }));
     }
@@ -145,7 +145,7 @@ public sealed partial class SearchBar : UserControl,
                 // hack TODO GH #245
                 if (CurrentPageViewModel is not null)
                 {
-                    CurrentPageViewModel.Filter = FilterBox.Text;
+                    CurrentPageViewModel.SearchTextBox = FilterBox.Text;
                 }
             }
 
@@ -156,7 +156,7 @@ public sealed partial class SearchBar : UserControl,
             // hack TODO GH #245
             if (CurrentPageViewModel is not null)
             {
-                CurrentPageViewModel.Filter = FilterBox.Text;
+                CurrentPageViewModel.SearchTextBox = FilterBox.Text;
             }
         }
     }
@@ -320,7 +320,7 @@ public sealed partial class SearchBar : UserControl,
         // Actually plumb Filtering to the view model
         if (CurrentPageViewModel is not null)
         {
-            CurrentPageViewModel.Filter = FilterBox.Text;
+            CurrentPageViewModel.SearchTextBox = FilterBox.Text;
         }
     }