Migrate desktop_photo_search to top level (#1002)

desktop_photo_search/fluent_ui/lib/unsplash_access_key.dart

@@ -0,0 +1,9 @@
+// Copyright 2019 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// TODO: Retrieve an API Access Key from https://unsplash.com/developers
+const String unsplashAccessKey = '';
+
+// The application name for the above API Access Key.
+const unsplashAppName = '';