CmdPal: Bind FilterDropDown selection to the current filter and ensure notifications are raised on UI thread (#41808)

## Summary of the Pull Request

This PR declaratively binds FilterDropDown.SelectedValue to
CurrentFilterId (one-way only; updates in the opposite direction are
handled within the drop-down’s code). It also removes observable
properties and reverts to the UpdateProperty style to ensure property
change notifications are raised on the UI thread, aligning the handling
style with other classes.

## Impact
- Fixed a crash that could occur on pages with filters
- The filter drop-down now correctly syncs with the initially selected
filter when loading a page

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## PR Checklist

- [x] Closes: #41578
- [x] Closes: #41649
- [ ] **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.Core.ViewModels/ExtensionObjectViewModel.cs

@@ -51,6 +51,36 @@ public abstract partial class ExtensionObjectViewModel : ObservableObject
         DoOnUiThread(() => OnPropertyChanged(propertyName));
     }
 
+    protected void UpdateProperty(string propertyName1, string propertyName2)
+    {
+        DoOnUiThread(() =>
+        {
+            OnPropertyChanged(propertyName1);
+            OnPropertyChanged(propertyName2);
+        });
+    }
+
+    protected void UpdateProperty(string propertyName1, string propertyName2, string propertyName3)
+    {
+        DoOnUiThread(() =>
+        {
+            OnPropertyChanged(propertyName1);
+            OnPropertyChanged(propertyName2);
+            OnPropertyChanged(propertyName3);
+        });
+    }
+
+    protected void UpdateProperty(params string[] propertyNames)
+    {
+        DoOnUiThread(() =>
+        {
+            foreach (var propertyName in propertyNames)
+            {
+                OnPropertyChanged(propertyName);
+            }
+        });
+    }
+
     protected void ShowException(Exception ex, string? extensionHint = null)
     {
         if (PageContext.TryGetTarget(out var pageContext))

src/modules/cmdpal/Microsoft.CmdPal.Core.ViewModels/FiltersViewModel.cs

@@ -2,7 +2,6 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using CommunityToolkit.Mvvm.ComponentModel;
 using Microsoft.CmdPal.Core.ViewModels.Models;
 using Microsoft.CommandPalette.Extensions;
 
@@ -10,14 +9,11 @@ namespace Microsoft.CmdPal.Core.ViewModels;
 
 public partial class FiltersViewModel : ExtensionObjectViewModel
 {
-    private readonly ExtensionObject<IFilters> _filtersModel = new(null);
+    private readonly ExtensionObject<IFilters> _filtersModel;
 
-    [ObservableProperty]
-    public partial string CurrentFilterId { get; set; } = string.Empty;
+    public string CurrentFilterId { get; private set; } = string.Empty;
 
-    [ObservableProperty]
-    [NotifyPropertyChangedFor(nameof(ShouldShowFilters))]
-    public partial IFilterItemViewModel[] Filters { get; set; } = [];
+    public IFilterItemViewModel[] Filters { get; private set; } = [];
 
     public bool ShouldShowFilters => Filters.Length > 0;
 
@@ -34,23 +30,11 @@ public partial class FiltersViewModel : ExtensionObjectViewModel
             if (_filtersModel.Unsafe is not null)
             {
                 var filters = _filtersModel.Unsafe.GetFilters();
-                Filters = filters.Select<IFilterItem, IFilterItemViewModel>(filter =>
-                {
-                    var filterItem = filter as IFilter;
-                    if (filterItem != null)
-                    {
-                        var filterVM = new FilterItemViewModel(filterItem!, PageContext);
-                        filterVM.InitializeProperties();
+                Filters = BuildFilters(filters ?? []);
+                UpdateProperty(nameof(Filters), nameof(ShouldShowFilters));
 
-                        return filterVM;
-                    }
-                    else
-                    {
-                        return new SeparatorViewModel();
-                    }
-                }).ToArray();
-
-                CurrentFilterId = _filtersModel.Unsafe.CurrentFilterId;
+                CurrentFilterId = _filtersModel.Unsafe.CurrentFilterId ?? string.Empty;
+                UpdateProperty(nameof(CurrentFilterId));
 
                 return;
             }
@@ -61,7 +45,27 @@ public partial class FiltersViewModel : ExtensionObjectViewModel
         }
 
         Filters = [];
+        UpdateProperty(nameof(Filters), nameof(ShouldShowFilters));
+
         CurrentFilterId = string.Empty;
+        UpdateProperty(nameof(CurrentFilterId));
+    }
+
+    private IFilterItemViewModel[] BuildFilters(IFilterItem[] filters)
+    {
+        return [..filters.Select<IFilterItem, IFilterItemViewModel>(filter =>
+        {
+            if (filter is IFilter filterItem)
+            {
+                var filterItemViewModel = new FilterItemViewModel(filterItem!, PageContext);
+                filterItemViewModel.InitializeProperties();
+                return filterItemViewModel;
+            }
+            else
+            {
+                return new SeparatorViewModel();
+            }
+        })];
     }
 
     public override void SafeCleanup()
@@ -70,9 +74,9 @@ public partial class FiltersViewModel : ExtensionObjectViewModel
 
         foreach (var filter in Filters)
         {
-            if (filter is FilterItemViewModel filterVM)
+            if (filter is FilterItemViewModel filterItemViewModel)
             {
-                filterVM.SafeCleanup();
+                filterItemViewModel.SafeCleanup();
             }
         }
 

src/modules/cmdpal/Microsoft.CmdPal.UI/Controls/FiltersDropDown.xaml

@@ -74,6 +74,8 @@
         ItemsSource="{x:Bind ViewModel.Filters, Mode=OneWay}"
         PlaceholderText="Filters"
         PreviewKeyDown="FiltersComboBox_PreviewKeyDown"
+        SelectedValue="{x:Bind ViewModel.CurrentFilterId, Mode=OneWay}"
+        SelectedValuePath="Id"
         SelectionChanged="FiltersComboBox_SelectionChanged"
         Style="{StaticResource ComboBoxStyle}"
         Visibility="{x:Bind ViewModel.ShouldShowFilters, Mode=OneWay, Converter={StaticResource BoolToVisibilityConverter}}">