[modules] Implement namespace imports.

test/mjsunit/modules-namespace4.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.
+//
+// MODULE
+
+import * as foo from "modules-namespace4.js";
+
+assertSame(undefined, a);
+assertThrows(() => b, ReferenceError);
+assertThrows(() => c, ReferenceError);
+assertEquals(45, d());
+
+assertSame(undefined, foo.a);
+assertThrows(() => foo.b, ReferenceError);
+assertThrows(() => foo.c, ReferenceError);
+assertEquals(45, foo.d());
+assertThrows(() => foo.default, ReferenceError);
+assertSame(undefined, foo.doesnotexist);
+
+export var a = 42;
+export let b = 43;
+export const c = 44;
+export function d() { return 45 };
+export default 46;
+
+assertEquals(42, a);
+assertEquals(43, b);
+assertEquals(44, c);
+assertEquals(45, d());
+
+assertEquals(42, foo.a);
+assertEquals(43, foo.b);
+assertEquals(44, foo.c);
+assertEquals(45, foo.d());
+assertEquals(46, foo.default);
+assertSame(undefined, foo.doesnotexist);