Create remote file browser service (#448)

* code refactoring

* Add filebrowser service and tests

* change dataset reference

* Address pr comments

* add more tests

* address pr comments

* address pr comments and added more tests

* minor change

* minor fix

* Fix test break and add dataset result check

src/Microsoft.SqlTools.ServiceLayer/FileBrowser/Contracts/FileBrowserExpandRequest.cs

@@ -0,0 +1,34 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+using Microsoft.SqlTools.Hosting.Protocol.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.FileBrowser.Contracts
+{
+    /// <summary>
+    /// Parameters for expanding a folder node
+    /// </summary>
+    public class FileBrowserExpandParams
+    {
+        /// <summary>
+        /// Connection uri
+        /// </summary>
+        public string OwnerUri;
+
+        /// <summary>
+        /// The path to expand the nodes for
+        /// </summary>
+        public string ExpandPath;
+    }
+
+    /// <summary>
+    /// Request to expand a node in the file browser
+    /// </summary>
+    public class FileBrowserExpandRequest
+    {
+        public static readonly
+            RequestType<FileBrowserExpandParams, bool> Type =
+                RequestType<FileBrowserExpandParams, bool>.Create("filebrowser/expand");
+    }
+}