[Settings]Fix backup and restore select folder when running as admin (#24164)

* Settings bkp and restore
Open foolder when elevated using shell32 api.

* increase the size of the alocated buffer for the path
based on https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=registry

src/settings-ui/Settings.UI/Helpers/ShellGetFolder.cs

@@ -0,0 +1,72 @@
+// 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.Runtime.InteropServices;
+using System.Text;
+using static Microsoft.PowerToys.Settings.UI.Helpers.ShellGetFolder;
+
+namespace Microsoft.PowerToys.Settings.UI.Helpers
+{
+    public class ShellGetFolder
+    {
+        [DllImport("shell32.dll")]
+        private static extern IntPtr SHBrowseForFolderW(ref BrowseInformation browseInfo);
+
+        [DllImport("shell32.dll")]
+        private static extern int SHGetPathFromIDListW(IntPtr pidl, IntPtr pszPath);
+
+        public delegate int BrowseCallbackProc(IntPtr hwnd, int msg, IntPtr lp, IntPtr wp);
+
+        [StructLayout(LayoutKind.Sequential)]
+        public struct BrowseInformation
+        {
+            public IntPtr HwndOwner;
+            public IntPtr PidlRoot;
+            public string PszDisplayName;
+            public string LpszTitle;
+            public uint UlFlags;
+            public BrowseCallbackProc Lpfn;
+            public IntPtr LParam;
+            public int IImage;
+        }
+
+        public static string GetFolderDialog(IntPtr hwndOwner)
+        {
+            // windows MAX_PATH with long path enable can be approximated 32k char long
+            // allocating more than double (unicode) to hold the path
+            StringBuilder sb = new StringBuilder(65000);
+            IntPtr bufferAddress = Marshal.AllocHGlobal(65000);
+            IntPtr pidl = IntPtr.Zero;
+            BrowseInformation browseInfo;
+            browseInfo.HwndOwner = hwndOwner;
+            browseInfo.PidlRoot = IntPtr.Zero;
+            browseInfo.PszDisplayName = null;
+            browseInfo.LpszTitle = null;
+            browseInfo.UlFlags = 0;
+            browseInfo.Lpfn = null;
+            browseInfo.LParam = IntPtr.Zero;
+            browseInfo.IImage = 0;
+
+            try
+            {
+                pidl = SHBrowseForFolderW(ref browseInfo);
+                if (SHGetPathFromIDListW(pidl, bufferAddress) == 0)
+                {
+                    return null;
+                }
+
+                sb.Append(Marshal.PtrToStringUni(bufferAddress));
+                Marshal.FreeHGlobal(bufferAddress);
+            }
+            finally
+            {
+                // Need to free pidl
+                Marshal.FreeCoTaskMem(pidl);
+            }
+
+            return sb.ToString();
+        }
+    }
+}