Create goog.module from module d.ts files

[evmar]

When given a module d.ts file, e.g.

export type A = ...;
declare global {
  type B = ...;
}

tsickle needs to emit two files:

//////// file 1: externs
/** @externs */
/** @typedef or whatever */
const A;

/** @typedef or whatever */
const mangled$name$B;

//////// file 2: module
goog.module('module.name');
exports.B = mangled$name$B;

tsickle currently correctly emits the first file, but leaves out the second module file. The second file is needed so that users that import this d.ts can refer to module.name.B in type annotations.

If there are any values inside the module, tsickle should just drop them for now, because there's no way to alias a value in a module.

questions

Do we need to create an alias for each export? Or will something like exports = mangled$name; be sufficient? Will likely need an experiment.

[mprobst]

Another question: how do we handle .d.ts files that declare values, not just types? Currently we don't generate anything and expect the user to supply a shim.

[evmar]

This is basically a dup of the longer #1041 .