Import types in JS with var x = require('./mod')

[sandersn]

Fixes #11825

Previously, in Javascript, you could reference types by importing them from a Typescript file:

// Filename: types.d.ts
export type Type = { a, b, c }

// Filename: use.js
import * as mod from './mod'
/** @type {mod.Type} */
var t;

But this didn't work with var = require('./mod') syntax. Now it does:

// Filename: types.d.ts
export type Type = { a, b, c }

// Filename: use.js
var mod = require('./mod')
/** @type {mod.Type} */
var t;

You can also now use the types of classes, both from Typescript and Javascript:

// Filename: pg.js
export class Pool {
  m() {
  }
}

// Filename: use.js
var pg = require('./pg')
/** @type {pg.Pool} */
var pool;

[sandersn]

@aozgaa @DanielRosenwasser you were interested in this PR too I believe.

[sandersn]

this is just a drive-by fix — you can see that the else clause will never happen based on the containing if.