Reland: [modules] Properly initialize declared variables.

test/mjsunit/modules-skip-init3.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import {v, w, x, y, z} from "modules-init3.js";
+
+assertEquals({value: 40, done: true}, v().next());
+assertSame(undefined, w);
+assertThrows(() => x, ReferenceError);
+assertThrows(() => y, ReferenceError);
+assertThrows(() => z, ReferenceError);
+
+export function check() {
+  assertEquals({value: 40, done: true}, v().next());
+  assertEquals(41, w);
+  assertEquals(42, x);
+  assertEquals("y", y.name);
+  assertEquals("hello world", z);
+  return true;
+}