[cmdpal] Add Open URL fallback command for WebSearch ext (#38685)

## Summary of the Pull Request
1. Add new fallback command for websearch

https://github.com/user-attachments/assets/39362d66-db59-42d4-b07c-7bfd60b2e420

## PR Checklist

- [x] **Closes:** #38497

---------

Co-authored-by: Yu Leng (from Dev Box) <yuleng@microsoft.com>

src/modules/cmdpal/Exts/Microsoft.CmdPal.Ext.WebSearch/FallbackOpenURLItem.cs

@@ -0,0 +1,88 @@
+// 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.Globalization;
+using System.Text;
+using Microsoft.CmdPal.Ext.WebSearch.Commands;
+using Microsoft.CmdPal.Ext.WebSearch.Helpers;
+using Microsoft.CmdPal.Ext.WebSearch.Properties;
+using Microsoft.CommandPalette.Extensions.Toolkit;
+using BrowserInfo = Microsoft.CmdPal.Ext.WebSearch.Helpers.DefaultBrowserInfo;
+
+namespace Microsoft.CmdPal.Ext.WebSearch;
+
+internal sealed partial class FallbackOpenURLItem : FallbackCommandItem
+{
+    private readonly OpenURLCommand _executeItem;
+    private static readonly CompositeFormat PluginOpenURL = System.Text.CompositeFormat.Parse(Properties.Resources.plugin_open_url);
+    private static readonly CompositeFormat PluginOpenUrlInBrowser = System.Text.CompositeFormat.Parse(Properties.Resources.plugin_open_url_in_browser);
+
+    public FallbackOpenURLItem(SettingsManager settings)
+        : base(new OpenURLCommand(string.Empty, settings), string.Empty)
+    {
+        _executeItem = (OpenURLCommand)this.Command!;
+        Title = string.Empty;
+        _executeItem.Name = string.Empty;
+        Subtitle = string.Empty;
+        Icon = IconHelpers.FromRelativePath("Assets\\WebSearch.png");
+    }
+
+    public override void UpdateQuery(string query)
+    {
+        if (!IsValidUrl(query))
+        {
+            Title = string.Empty;
+            Subtitle = string.Empty;
+            return;
+        }
+
+        var success = Uri.TryCreate(query, UriKind.Absolute, out var uri);
+
+        // if url not contain schema, add http:// by default.
+        if (!success)
+        {
+            query = "https://" + query;
+        }
+
+        _executeItem.Url = query;
+        _executeItem.Name = string.IsNullOrEmpty(query) ? string.Empty : Properties.Resources.open_in_default_browser;
+
+        Title = string.Format(CultureInfo.CurrentCulture, PluginOpenURL, query);
+        Subtitle = string.Format(CultureInfo.CurrentCulture, PluginOpenUrlInBrowser, BrowserInfo.Name ?? BrowserInfo.MSEdgeName);
+    }
+
+    public static bool IsValidUrl(string url)
+    {
+        if (string.IsNullOrWhiteSpace(url))
+        {
+            return false;
+        }
+
+        if (!url.Contains('.', StringComparison.OrdinalIgnoreCase))
+        {
+            // eg: 'com', 'org'. We don't think it's a valid url.
+            // This can simplify the logic of checking if the url is valid.
+            return false;
+        }
+
+        if (Uri.IsWellFormedUriString(url, UriKind.Absolute))
+        {
+            return true;
+        }
+
+        if (!url.StartsWith("http://", StringComparison.OrdinalIgnoreCase) &&
+            !url.StartsWith("https://", StringComparison.OrdinalIgnoreCase) &&
+            !url.StartsWith("ftp://", StringComparison.OrdinalIgnoreCase) &&
+            !url.StartsWith("file://", StringComparison.OrdinalIgnoreCase))
+        {
+            if (Uri.IsWellFormedUriString("https://" + url, UriKind.Absolute))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}