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/UpdateManagement/RowUpdate.cs

@@ -113,6 +113,30 @@ namespace Microsoft.SqlTools.ServiceLayer.EditData.UpdateManagement
             return command;
         }
 
+        /// <summary>
+        /// Generates a edit row that represents a row with pending update. The cells pending
+        /// updates are merged into the unchanged cells.
+        /// </summary>
+        /// <param name="cachedRow">Original, cached cell contents</param>
+        /// <returns>EditRow with pending updates</returns>
+        public override EditRow GetEditRow(DbCellValue[] cachedRow)
+        {
+            Validate.IsNotNull(nameof(cachedRow), cachedRow);
+
+            // For each cell that is pending update, replace the db cell value with a new one
+            foreach (var cellUpdate in cellUpdates)
+            {
+                cachedRow[cellUpdate.Key] = cellUpdate.Value.AsDbCellValue;
+            }
+
+            return new EditRow
+            {
+                Id = RowId,
+                Cells = cachedRow,
+                State = EditRow.EditRowState.DirtyUpdate
+            };
+        }
+
         /// <summary>
         /// Constructs an update statement to change the associated row.
         /// </summary>