CmdPal: Add settings to control which fallbacks are enabled (#40505)

This adds settings to each provider to allow us to control if individual
fallback items are enabled or not, regardless of the provider being
enabled.

This is relevant to _all the threads where disabling fallback commands
came up_

This just adds another section to each provider's settings page, with a
list of the fallback commands.

This also has nothing to do with the "top-level apps search", which is
not really a fallback command - it's its own thing.

Ref #38288. Doesn't close that, because this only controls
enable/disable, not ranking.

From here, we should be able to add a dedicated page in the SUI that
shows all the fallbacks across all providers. That's where we'll enable
the ordering.

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/TopLevelViewModel.cs

@@ -4,7 +4,9 @@
 
 using System.Collections.ObjectModel;
 using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Messaging;
 using ManagedCommon;
+using Microsoft.CmdPal.UI.ViewModels.Messages;
 using Microsoft.CmdPal.UI.ViewModels.Settings;
 using Microsoft.CommandPalette.Extensions;
 using Microsoft.CommandPalette.Extensions.Toolkit;
@@ -17,6 +19,7 @@ namespace Microsoft.CmdPal.UI.ViewModels;
 public sealed partial class TopLevelViewModel : ObservableObject, IListItem
 {
     private readonly SettingsModel _settings;
+    private readonly ProviderSettings _providerSettings;
     private readonly IServiceProvider _serviceProvider;
     private readonly CommandItemViewModel _commandItemViewModel;
 
@@ -77,6 +80,9 @@ public sealed partial class TopLevelViewModel : ObservableObject, IListItem
     ////// INotifyPropChanged
     public event TypedEventHandler<object, IPropChangedEventArgs>? PropChanged;
 
+    // Fallback items
+    public string DisplayTitle { get; private set; } = string.Empty;
+
     public HotkeySettings? Hotkey
     {
         get => _hotkey;
@@ -133,16 +139,32 @@ public sealed partial class TopLevelViewModel : ObservableObject, IListItem
         }
     }
 
+    public bool IsEnabled
+    {
+        get => _providerSettings.IsFallbackEnabled(this);
+        set
+        {
+            if (value != IsEnabled)
+            {
+                _providerSettings.SetFallbackEnabled(this, value);
+                Save();
+                WeakReferenceMessenger.Default.Send<ReloadCommandsMessage>(new());
+            }
+        }
+    }
+
     public TopLevelViewModel(
         CommandItemViewModel item,
         bool isFallback,
         CommandPaletteHost extensionHost,
         string commandProviderId,
         SettingsModel settings,
+        ProviderSettings providerSettings,
         IServiceProvider serviceProvider)
     {
         _serviceProvider = serviceProvider;
         _settings = settings;
+        _providerSettings = providerSettings;
         _commandProviderId = commandProviderId;
         _commandItemViewModel = item;
 
@@ -156,6 +178,22 @@ public sealed partial class TopLevelViewModel : ObservableObject, IListItem
         // UpdateTags();
     }
 
+    internal void InitializeProperties()
+    {
+        ItemViewModel.SlowInitializeProperties();
+
+        if (IsFallback)
+        {
+            var model = _commandItemViewModel.Model.Unsafe;
+
+            // RPC to check type
+            if (model is IFallbackCommandItem fallback)
+            {
+                DisplayTitle = fallback.DisplayTitle;
+            }
+        }
+    }
+
     private void Item_PropertyChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)
     {
         if (!string.IsNullOrEmpty(e.PropertyName))
@@ -240,7 +278,7 @@ public sealed partial class TopLevelViewModel : ObservableObject, IListItem
     {
         // Use WyHash64 to generate stable ID hashes.
         // manually seeding with 0, so that the hash is stable across launches
-        var result = WyHash64.ComputeHash64(_commandProviderId + Title + Subtitle, seed: 0);
+        var result = WyHash64.ComputeHash64(_commandProviderId + DisplayTitle + Title + Subtitle, seed: 0);
         _generatedId = $"{_commandProviderId}{result}";
     }
 
@@ -263,6 +301,11 @@ public sealed partial class TopLevelViewModel : ObservableObject, IListItem
             return false;
         }
 
+        if (!IsEnabled)
+        {
+            return false;
+        }
+
         try
         {
             return UnsafeUpdateFallbackSynchronous(newQuery);