Merge pull request #9997 from Microsoft/re-add-strict-concat-signature

Re-add strict concat signature

src/lib/es5.d.ts

@@ -1108,6 +1108,11 @@ interface Array<T> {
       * Removes the last element from an array and returns it.
       */
     pop(): T | undefined;
+    /**
+      * Combines two or more arrays.
+      * @param items Additional items to add to the end of array1.
+      */
+    concat(...items: T[][]): T[];
     /**
       * Combines two or more arrays.
       * @param items Additional items to add to the end of array1.