Declaration file emitted with esModuleInterop can't be consumed without it

**TypeScript Version:** 3.2.0-dev.20181019 **Search Terms:** **Code** ```ts import abs from "abs"; // using @types/abs which uses `export =` export const x: typeof abs = <any>null; ``` **Expected behavior:** Output `.d.ts` is: ```ts import abs = require("abs"); export declare const x: typeof abs; ``` **Actual behavior:** ```ts import abs from "abs"; export declare const x: typeof abs; ``` Discovered in `quill` on DefinitelyTyped, which imports from `quill-delta`, which is [written in TypeScript](https://github.com/quilljs/delta/blob/master/src/Delta.ts) with `esModuleInterop`.