Display Drive detection warning only for multiple drives (#7589)

* indexer drive detection helper code to not show the warning for a single drive

* removed interface from the namespace due to stylecop

* removed interfac which no longer exists

* filter out only fixed drives in the system and ignore the removable drives

* changed text to not all files are indexed, from not all drives are idnexed

* add additional info in the comment

src/modules/launcher/Plugins/Microsoft.Plugin.Indexer/Interface/IDriveInfoWrapper.cs

@@ -0,0 +1,11 @@
+// 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.
+
+namespace Microsoft.Plugin.Indexer
+{
+    public interface IDriveInfoWrapper
+    {
+        int GetDriveCount();
+    }
+}