Support for type destructuring

TypeScript Version: 2.1.4

Code

import { MyNamespace } from 'my-package';

// importing Class objects:
const { NavLink, NavGroup } = MyNamespace; // VALID

// if we want the types as well:
type { NavLink, NavGroup } = MyNamespace; // NOT VALID

// So we have to go manual: 
type NavLink = MyNamespace.NavLink;  // VALID
type NavGroup = MyNamespace.NavLink;  // VALID

Expected behavior:
Being able to use destructuring for types same as we use for objects.

Actual behavior:
Can only use destructuring for objects.

该 issue 没有提供可供开始的 repository 文件、测试或入口点。先复现 TypeScript 2.1.4 示例，然后跟踪 object destructuring 和 type aliases 的解析与检查方式。当 type destructuring 能够在所示的 namespace 示例中正常工作，具备适当的 compiler 覆盖，并且不会导致 object destructuring 回归时，即视为完成。