Add a contextual type in test case

Author: mhegazy

tests/cases/fourslash/renameStingLiterals.ts

@@ -1,5 +1,6 @@
 /// <reference path='fourslash.ts' />
 
+////var y: "string" = "string;
 ////var x = "/*1*/string";
 ////function f(a = "/*2*/initial value") { }