Introduce getSynthesizedDeepClone

src/compiler/factory.ts

@@ -71,6 +71,15 @@ namespace ts {
         return clone;
     }
 
+    /**
+     * Creates a deep, memberwise clone of a node with no source map location.
+     */
+    export function getSynthesizedDeepClone<T extends Node>(node: T | undefined): T | undefined {
+        return node
+            ? getSynthesizedClone(visitEachChild(node, child => getSynthesizedDeepClone(child), nullTransformationContext))
+            : undefined;
+    }
+
     // Literals
 
     export function createLiteral(value: string): StringLiteral;