[CmdPal] Fix filters visibility on non-ListPage (#42828)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request
This PR aims to fix the issue where filters from a ListPage remain
visible when navigating to other pages.
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## PR Checklist

- [x] Closes: #42827 
- [ ] **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
### Before:

![FiltersIssue](https://github.com/user-attachments/assets/b0ad6059-9a11-4e12-821d-7202358e25bb)

### After:

![FiltersFix](https://github.com/user-attachments/assets/b9ee71ee-cb5d-4ef9-b9fc-bc2e2a710b5c)

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

---------

Co-authored-by: Jiří Polášek <me@jiripolasek.com>

src/modules/cmdpal/ext/SamplePagesExtension/Pages/IssueSpecificPages/AllIssueSamplesIndexPage.cs

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.CommandPalette.Extensions;
+using Microsoft.CommandPalette.Extensions.Toolkit;
+
+namespace SamplePagesExtension.Pages.IssueSpecificPages;
+
+internal sealed partial class AllIssueSamplesIndexPage : ListPage
+{
+    public AllIssueSamplesIndexPage()
+    {
+        Icon = new IconInfo("🐛");
+        Name = "All Issue Samples Index Page";
+    }
+
+    public override IListItem[] GetItems()
+    {
+        return new IListItem[]
+        {
+            new ListItem(new SamplePageForIssue42827_FilterDropDownStaysVisibleAfterSwitchingFromListToContentPage())
+            {
+                Title = "Issue 42827 - Filter Drop Down Stays Visible After Switching From List To Content Page",
+                Subtitle = "Repro steps: Open this page, open the filter dropdown, select a filter, navigate to a content page, navigate back to this page. The filter dropdown should be closed but it remains open.",
+            },
+        };
+    }
+}

src/modules/cmdpal/ext/SamplePagesExtension/Pages/IssueSpecificPages/SamplePageForIssue42827_FilterDropDownStaysVisibleAfterSwitchingFromListToContentPage.cs

@@ -0,0 +1,76 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Linq;
+using Microsoft.CommandPalette.Extensions;
+using Microsoft.CommandPalette.Extensions.Toolkit;
+
+namespace SamplePagesExtension.Pages.IssueSpecificPages;
+
+internal sealed partial class SamplePageForIssue42827_FilterDropDownStaysVisibleAfterSwitchingFromListToContentPage : DynamicListPage
+{
+    public SamplePageForIssue42827_FilterDropDownStaysVisibleAfterSwitchingFromListToContentPage()
+    {
+        Icon = new IconInfo(string.Empty);
+        Name = "Issue 42827 - Filters not hiding when navigating between pages";
+        IsLoading = true;
+        var filters = new SampleFilters();
+        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()
+    {
+        var items = SearchText.ToCharArray().Select(ch => new ListItem(new SampleContentPage()) { Title = ch.ToString() }).ToArray();
+        if (items.Length == 0)
+        {
+            items = [
+                new ListItem(new SampleContentPage()) { Title = "This List item will open a content page" },
+                new ListItem(new SampleContentPage()) { Title = "This List item will open a content page too" },
+                new ListItem(new SampleContentPage()) { Title = "Guess what this one will do?" },
+            ];
+        }
+
+        if (!string.IsNullOrEmpty(Filters.CurrentFilterId))
+        {
+            switch (Filters.CurrentFilterId)
+            {
+                case "mod2":
+                    items = items.Where((item, index) => (index + 1) % 2 == 0).ToArray();
+                    break;
+                case "mod3":
+                    items = items.Where((item, index) => (index + 1) % 3 == 0).ToArray();
+                    break;
+                case "all":
+                default:
+                    // No filtering
+                    break;
+            }
+        }
+
+        foreach (var item in items)
+        {
+            item.Subtitle = "Filter drop-down should be hidden when navigating to a content page";
+        }
+
+        return items;
+    }
+
+    internal sealed partial class SampleFilters : Filters
+    {
+        public override IFilterItem[] GetFilters()
+        {
+            return
+            [
+                new Filter() { Id = "all", Name = "All" },
+                new Filter() { Id = "mod2", Name = "Every 2nd", Icon = new IconInfo("2") },
+                new Filter() { Id = "mod3", Name = "Every 3rd (and long name)", Icon = new IconInfo("3") },
+            ];
+        }
+    }
+}

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

@@ -5,6 +5,7 @@
 using Microsoft.CommandPalette.Extensions;
 using Microsoft.CommandPalette.Extensions.Toolkit;
 using SamplePagesExtension.Pages;
+using SamplePagesExtension.Pages.IssueSpecificPages;
 
 namespace SamplePagesExtension;
 
@@ -106,6 +107,11 @@ public partial class SamplesListPage : ListPage
         {
             Title = "Evil samples",
             Subtitle = "Samples designed to break the palette in many different evil ways",
+        },
+        new ListItem(new AllIssueSamplesIndexPage())
+        {
+            Title = "Issue-specific samples",
+            Subtitle = "Samples designed to reproduce specific issues",
         }
     ];