jszip usage breaks for projects that use @babel/preset-env

[icopp]

• jszip uses a require("core-js/library/fn/set-immediate") statement at one point
• A Babel build with @babel/preset-env and "useBuiltIns": "entry" uses a custom-minified version of core-js including only the polyfills needed to make the list of that project's supported browsers work
• The resulting bundle doesn't include setImmediate (because nothing in the bundle actually references setImmediate as a global function)
• ...which leads to jszip breaking, because it's trying to require something not in the bundle

The "right" behavior here would be to either (a) just use setImmediate directly, and leave it up to the end user as to whether they want to use the polyfill, or (b) use a standalone setImmediate ponyfill instead of pulling in the entire core-js library.

[RinkAttendant6]

It looks like the core-js dependency was replaced with set-immediate-shim in #532.