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/FileBrowserValidateEventArgs.cs

@@ -0,0 +1,30 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+
+namespace Microsoft.SqlTools.ServiceLayer.FileBrowser
+{
+    /// <summary>
+    /// Event arguments for validating selected files in file browser
+    /// </summary>
+    public sealed class FileBrowserValidateEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Connection uri
+        /// </summary>
+        public string OwnerUri { get; set; }
+
+        /// <summary>
+        /// Service which provide validation callback
+        /// </summary>
+        public string ServiceType { get; set; }
+
+        /// <summary>
+        /// Selected files
+        /// </summary>
+        public string[] FilePaths { get; set; }
+    }
+}