feature/edit/subset (#283)

* Changing query/subset API to only use Result on success, Error on error

* Creating an interservice API for getting query result subsets

* Updates to subset API

* RowStartIndex is now long
* Output of query/subset is a 2D array of DbCellValue
* Adding LongSkip method to LongList to allow skipping ahead by longs
* Moving LongList back to ServiceLayer utilities. Move refactoring

* Stubbing out request for edit/subset

* Initial implementation of getting edit rows

* Unit tests for RowEdit and RowDelete .GetEditRow

* Fixing major bugs in LongList implementation, adding much more thorough tests

* Adding some more unit tests and fixes to make unit tests pass

* Fixing comment

src/Microsoft.SqlTools.ServiceLayer/EditData/Contracts/EditRow.cs

@@ -0,0 +1,45 @@
+//
+// 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.ServiceLayer.QueryExecution.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.EditData.Contracts
+{
+    /// <summary>
+    /// A way to return a row in a result set that is being edited. It contains state about whether
+    /// or not the row is dirty
+    /// </summary>
+    public class EditRow
+    {
+        public enum EditRowState
+        {
+            Clean = 0,
+            DirtyInsert = 1,
+            DirtyDelete = 2,
+            DirtyUpdate = 3
+        }
+
+        /// <summary>
+        /// The cells in the row. If the row has pending changes, they will be represented in
+        /// this list
+        /// </summary>
+        public DbCellValue[] Cells { get; set; }
+
+        /// <summary>
+        /// Internal ID of the row. This should be used whenever referencing a row in row edit operations.
+        /// </summary>
+        public long Id { get; set; }
+
+        /// <summary>
+        /// Whether or not the row has changes pending
+        /// </summary>
+        public bool IsDirty => State != EditRowState.Clean;
+
+        /// <summary>
+        /// What type of dirty state (or lack thereof) the row is
+        /// </summary>
+        public EditRowState State { get; set; }
+    }
+}