[Registry Preview] Moving to a different API to call the File Picker (#25260)

* Moving from FileOpenPicker

Moving from FileOpenPicker to a Win32/PInvoke version, so it can be opened while running as Admin.

* Update Resources.resw

Replacing a lost string.

* Save file picker also crashed

Switched to Win32-based SafeFilePicker
Cleaned up some of the code which should now pass spell checking and removed pragmas

src/modules/registrypreview/RegistryPreviewUI/OpenFileName.cs

@@ -0,0 +1,36 @@
+// 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.Runtime.InteropServices;
+
+namespace RegistryPreview
+{
+    // Workaround for File Pickers that don't work while running as admin, per:
+    // https://github.com/microsoft/WindowsAppSDK/issues/2504
+    public static partial class OpenFilePicker
+    {
+        [DllImport("comdlg32.dll", SetLastError = true, CharSet = CharSet.Auto)]
+        private static extern bool GetOpenFileName(ref FileName openFileName);
+
+        public static string ShowDialog(string filter, string dialogTitle)
+        {
+            FileName openFileName = default(FileName);
+            openFileName.StructSize = Marshal.SizeOf(openFileName);
+
+            openFileName.Filter = filter;
+            openFileName.File = new string(new char[256]);
+            openFileName.MaxFile = openFileName.File.Length;
+            openFileName.FileTitle = new string(new char[64]);
+            openFileName.MaxFileTitle = openFileName.FileTitle.Length;
+            openFileName.Title = dialogTitle;
+
+            if (GetOpenFileName(ref openFileName))
+            {
+                return openFileName.File;
+            }
+
+            return string.Empty;
+        }
+    }
+}