CmdPal: Add ability to refresh the list page while preserving selection (#45882)

## Summary of the Pull Request

This PR adds ability to invoke soft/incremental refresh that updates
items but keep selection in place (instead of resetting it to the first
item). For now, this is implemented as a hack using an unused parameter
of `ListPage.RaiseItemsChanged`: passing the constant `-2` tells the
view model that this is an incremental change and that it should keep
the current selection.


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## PR Checklist

- [x] Closes: #45694
- [x] Related to: #44407
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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

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI/ExtViews/ListPage.xaml.cs

@@ -231,25 +231,7 @@ public sealed partial class ListPage : Page,
         if (_scrollOnNextSelectionChange)
         {
             _scrollOnNextSelectionChange = false;
-
-            var scrollTarget = li;
-
-            // If the previous item is a separator, also scroll it into view to provide
-            // better context for the user
-            var index = ItemView.Items.IndexOf(li);
-            if (index > 0)
-            {
-                var prevItem = ItemView.Items[index - 1] as ListItemViewModel;
-                if (prevItem?.Type == ListItemType.SectionHeader)
-                {
-                    scrollTarget = prevItem;
-                }
-            }
-
-            if (scrollTarget is not null)
-            {
-                ItemView.ScrollIntoView(scrollTarget);
-            }
+            ScrollToItem(li);
         }
 
         // Automation notification for screen readers
@@ -263,6 +245,28 @@ public sealed partial class ListPage : Page,
         }
     }
 
+    private void ScrollToItem(ListItemViewModel li)
+    {
+        var scrollTarget = li;
+
+        // If the previous item is a separator, also scroll it into view to provide
+        // better context for the user
+        var index = ItemView.Items.IndexOf(li);
+        if (index > 0)
+        {
+            var prevItem = ItemView.Items[index - 1] as ListItemViewModel;
+            if (prevItem?.Type == ListItemType.SectionHeader)
+            {
+                scrollTarget = prevItem;
+            }
+        }
+
+        if (scrollTarget is not null)
+        {
+            ItemView.ScrollIntoView(scrollTarget);
+        }
+    }
+
     private void Items_RightTapped(object sender, RightTappedRoutedEventArgs e)
     {
         if (e.OriginalSource is FrameworkElement element &&
@@ -717,6 +721,8 @@ public sealed partial class ListPage : Page,
         {
             using (SuppressSelectionChangedScope())
             {
+                ListItemViewModel? stickyRestored = null;
+
                 if (!forceFirstItem &&
                     _stickySelectedItem is not null &&
                     items.Contains(_stickySelectedItem) &&
@@ -724,6 +730,7 @@ public sealed partial class ListPage : Page,
                 {
                     // Preserve sticky selection for nested dynamic updates.
                     ItemView.SelectedItem = _stickySelectedItem;
+                    stickyRestored = _stickySelectedItem;
                 }
                 else
                 {
@@ -741,7 +748,26 @@ public sealed partial class ListPage : Page,
                         return;
                     }
 
-                    ResetScrollToTop();
+                    if (stickyRestored is not null)
+                    {
+                        ScrollToItem(stickyRestored);
+                    }
+                    else
+                    {
+                        ResetScrollToTop();
+                    }
+                });
+            }
+        }
+        else
+        {
+            // Selection is valid and unchanged, just make sure the item is visible
+            if (_stickySelectedItem is ListItemViewModel li)
+            {
+                _ = DispatcherQueue.TryEnqueue(Microsoft.UI.Dispatching.DispatcherQueuePriority.Low, () =>
+                {
+                    ItemView.UpdateLayout();
+                    ScrollToItem(li);
                 });
             }
         }