Description of the change

purs bundle does not consider the dependencies of function declarations because the compiler always emit variable declarations. This has unfortunate consequences when optimizing foreign modules:

"use strict";

var x = 0;

function foo() {
  return x;
}

exports.foo = foo;

If the dependency of foo on x isn’t discovered, x appears unused and is removed from the bundle!

Fix #4039, fix #3259 and fix #2290.

Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)