edit/createRow Default Values (#266)

Returns strings for the default value of a column when a new row is created. The values that could come back:
* `null` when there isn't a default for the column
* a string when there is a default for the column
* a placeholder (currently <TBD>) when the column cannot be updated

* Renaming EditTableMetadata to reflect its SMO source

* Implementation of returning default values

* Unit test for default values

* Reworking column defaults using default constraints

* Adding unit test for new sql script unwrapper

* Disabling flaky test

* Fixing oddities in tests, removing personal tests

* Fixing broken unit test

src/Microsoft.SqlTools.ServiceLayer/EditData/EditDataService.cs

@@ -115,15 +115,7 @@ namespace Microsoft.SqlTools.ServiceLayer.EditData
         internal Task HandleCreateRowRequest(EditCreateRowParams createParams,
             RequestContext<EditCreateRowResult> requestContext)
         {
-            return HandleSessionRequest(createParams, requestContext, session =>
-            {
-                // Create the row and get the ID of the new row
-                long newRowId = session.CreateRow();
-                return new EditCreateRowResult
-                {
-                    NewRowId = newRowId
-                };
-            });
+            return HandleSessionRequest(createParams, requestContext, s => s.CreateRow());
         }
 
         internal Task HandleDeleteRowRequest(EditDeleteRowParams deleteParams,