CmdPal: Add drag & drop support (#44165)

## Summary of the Pull Request

This PR adds basic drag-and-drop support for items in list and grid
views.

It introduces two new properties on `ListItem`, backed by
`IExtendedAttributesProvider`: `DataPackage` and `DataPackageView`.
These properties are mutually exclusive.
`DataPackage` serves as a convenience property allowing the item to
retain the underlying object without risk of losing it. Across the
extension boundary, only the immutable `DataPackageView` snapshot is
transferred. When `DataPackage` is set, `DataPackageView` is derived
from it.

This PR includes initial concrete drag-and-drop implementations for:
- File Indexer  
- Clipboard History  

**Todo / Missing pieces** 
- [x] Extend `DataPackage` support to top-level command items, enabling
scenarios such as index fallback ~
- [x] Provide automatic drag-and-drop for unconfigured list items (e.g.,
copying title and subtitle as text)
- [x] Keep CmdPal open
- [ ] ~Clipboard commands (since we have the DataPackage...)~
- [ ] ~Improve logging~

## Pictures? Moving ones!


https://github.com/user-attachments/assets/13eb9a71-e760-43ea-8c2d-cd41cf377905




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## PR Checklist

- [x] Closes: #38289 
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
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/ext/Microsoft.CmdPal.Ext.Indexer/Data/IndexerListItem.cs

@@ -2,14 +2,17 @@
 // 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;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using Microsoft.CmdPal.Core.Common.Commands;
+using Microsoft.CmdPal.Ext.Indexer.Helpers;
 using Microsoft.CmdPal.Ext.Indexer.Pages;
 using Microsoft.CmdPal.Ext.Indexer.Properties;
 using Microsoft.CommandPalette.Extensions.Toolkit;
 using Windows.Foundation.Metadata;
+using FileAttributes = System.IO.FileAttributes;
 
 namespace Microsoft.CmdPal.Ext.Indexer.Data;
 
@@ -36,6 +39,8 @@ internal sealed partial class IndexerListItem : ListItem
         Title = indexerItem.FileName;
         Subtitle = indexerItem.FullPath;
 
+        DataPackage = DataPackageHelper.CreateDataPackageForPath(this, FilePath);
+
         var commands = FileCommands(indexerItem.FullPath, browseByDefault);
         if (commands.Any())
         {

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Indexer/FallbackOpenFileItem.cs

@@ -7,6 +7,7 @@ using System.Globalization;
 using System.IO;
 using System.Text;
 using Microsoft.CmdPal.Ext.Indexer.Data;
+using Microsoft.CmdPal.Ext.Indexer.Helpers;
 using Microsoft.CmdPal.Ext.Indexer.Properties;
 using Microsoft.CommandPalette.Extensions.Toolkit;
 using Windows.Storage.Streams;
@@ -42,6 +43,7 @@ internal sealed partial class FallbackOpenFileItem : FallbackCommandItem, System
             Subtitle = string.Empty;
             Icon = null;
             MoreCommands = null;
+            DataPackage = null;
 
             return;
         }
@@ -53,6 +55,7 @@ internal sealed partial class FallbackOpenFileItem : FallbackCommandItem, System
             Subtitle = string.Empty;
             Icon = null;
             MoreCommands = null;
+            DataPackage = null;
 
             return;
         }
@@ -67,6 +70,7 @@ internal sealed partial class FallbackOpenFileItem : FallbackCommandItem, System
             Subtitle = item.FileName;
             Title = item.FullPath;
             Icon = listItemForUs.Icon;
+            DataPackage = DataPackageHelper.CreateDataPackageForPath(listItemForUs, item.FullPath);
 
             try
             {
@@ -92,13 +96,15 @@ internal sealed partial class FallbackOpenFileItem : FallbackCommandItem, System
                 _searchEngine.Query(query, _queryCookie);
                 var results = _searchEngine.FetchItems(0, 20, _queryCookie, out var _);
 
-                if (results.Count == 0 || ((results[0] as IndexerListItem) is null))
+                if (results.Count == 0 || (results[0] is not IndexerListItem indexerListItem))
                 {
                     // Exit 2: We searched for the file, and found nothing. Oh well.
                     // Hide ourselves.
                     Title = string.Empty;
                     Subtitle = string.Empty;
                     Command = new NoOpCommand();
+                    MoreCommands = null;
+                    DataPackage = null;
                     return;
                 }
 
@@ -106,11 +112,12 @@ internal sealed partial class FallbackOpenFileItem : FallbackCommandItem, System
                 {
                     // Exit 3: We searched for the file, and found exactly one thing. Awesome!
                     // Return it.
-                    Title = results[0].Title;
-                    Subtitle = results[0].Subtitle;
-                    Icon = results[0].Icon;
-                    Command = results[0].Command;
-                    MoreCommands = results[0].MoreCommands;
+                    Title = indexerListItem.Title;
+                    Subtitle = indexerListItem.Subtitle;
+                    Icon = indexerListItem.Icon;
+                    Command = indexerListItem.Command;
+                    MoreCommands = indexerListItem.MoreCommands;
+                    DataPackage = DataPackageHelper.CreateDataPackageForPath(indexerListItem, indexerListItem.FilePath);
 
                     return;
                 }
@@ -121,6 +128,8 @@ internal sealed partial class FallbackOpenFileItem : FallbackCommandItem, System
                 Title = string.Format(CultureInfo.CurrentCulture, fallbackItemSearchPageTitleCompositeFormat, query);
                 Icon = Icons.FileExplorerIcon;
                 Command = indexerPage;
+                MoreCommands = null;
+                DataPackage = null;
 
                 return;
             }
@@ -131,6 +140,7 @@ internal sealed partial class FallbackOpenFileItem : FallbackCommandItem, System
                 Icon = null;
                 Command = new NoOpCommand();
                 MoreCommands = null;
+                DataPackage = null;
             }
         }
     }

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Indexer/Helpers/DataPackageHelper.cs

@@ -0,0 +1,64 @@
+// 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;
+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.CommandPalette.Extensions;
+using Windows.ApplicationModel.DataTransfer;
+using Windows.Storage;
+using File = System.IO.File;
+
+namespace Microsoft.CmdPal.Ext.Indexer.Helpers;
+
+internal static class DataPackageHelper
+{
+    public static DataPackage CreateDataPackageForPath(ICommandItem listItem, string path)
+    {
+        if (string.IsNullOrEmpty(path))
+        {
+            return null;
+        }
+
+        var dataPackage = new DataPackage();
+        dataPackage.SetText(path);
+        _ = dataPackage.TrySetStorageItemsAsync(path);
+        dataPackage.Properties.Title = listItem.Title;
+        dataPackage.Properties.Description = listItem.Subtitle;
+        dataPackage.RequestedOperation = DataPackageOperation.Copy;
+        return dataPackage;
+    }
+
+    public static async Task<bool> TrySetStorageItemsAsync(this DataPackage dataPackage, string filePath)
+    {
+        try
+        {
+            if (File.Exists(filePath))
+            {
+                var file = await StorageFile.GetFileFromPathAsync(filePath);
+                dataPackage.SetStorageItems([file]);
+                return true;
+            }
+
+            if (Directory.Exists(filePath))
+            {
+                var folder = await StorageFolder.GetFolderFromPathAsync(filePath);
+                dataPackage.SetStorageItems([folder]);
+                return true;
+            }
+
+            // nothing there
+            return false;
+        }
+        catch (UnauthorizedAccessException)
+        {
+            // Access denied – skip or report, but don't crash
+            return false;
+        }
+        catch (Exception)
+        {
+            return false;
+        }
+    }
+}

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Indexer/Pages/ExploreListItem.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using Microsoft.CmdPal.Core.Common.Commands;
 using Microsoft.CmdPal.Ext.Indexer.Data;
+using Microsoft.CmdPal.Ext.Indexer.Helpers;
 using Microsoft.CmdPal.Ext.Indexer.Properties;
 using Microsoft.CommandPalette.Extensions.Toolkit;
 using Windows.Foundation;
@@ -28,6 +29,9 @@ internal sealed partial class ExploreListItem : ListItem
 
         Title = indexerItem.FileName;
         Subtitle = indexerItem.FullPath;
+
+        DataPackage = DataPackageHelper.CreateDataPackageForPath(this, FilePath);
+
         List<CommandContextItem> context = [];
         if (indexerItem.IsDirectory())
         {