Handle `@extends` jsdoc tag

**TypeScript Version:**  nightly (2.5.0-dev.20170707)

**Code**

**C.d.ts**
```ts
export default class C<T> {
    t: T;
}
```

**D.js**
```js
import C from "./C";

/** @extends {C<number>} */
class D extends C {}

new D().t;
```

**Expected behavior:**

`t` is of type `number`.

**Actual behavior:**

`t` is of type `any`.

See also #17073.