Have MSSQL extension wait for SqlToolsService ready before finishing activation (#7087)

* Have mssql activate wait for service to be ready before returning

* Change to using deferred promise

* Await on server ready

* Finish removing old code

* More cleanup

* Go back to exposed promise API

* Make property readonly

* Add missing file

* Add back in deleted stuff

* Go back to awaiting

extensions/mssql/src/mssqlApiFactory.ts

@@ -27,6 +27,6 @@ export function createMssqlApi(context: AppContext): IExtension {
 					return <any>oeProvider.findSqlClusterNodeByContext(explorerContext);
 				}
 			};
-		},
+		}
 	};
 }