Migrate Java code to separate QL repo.

java/ql/src/Performance/NewStringString.ql

@@ -0,0 +1,18 @@
+/**
+ * @name Inefficient String constructor
+ * @description Using the 'String(String)' constructor is less memory efficient than using the
+ *              constructor argument directly.
+ * @kind problem
+ * @problem.severity recommendation
+ * @precision high
+ * @id java/inefficient-string-constructor
+ * @tags efficiency
+ *       maintainability
+ */
+import java
+
+from ClassInstanceExpr e
+where
+  e.getConstructor().getDeclaringType() instanceof TypeString and
+  e.getArgument(0).getType() instanceof TypeString
+select e, "Inefficient new String(String) constructor."