bundles es6 compatible code into the esm directory

[benjaminknox]

What?

I ran into an issue when bundling this app with an es6 app, my resulting packaged source included two threejs builds, three.module.js (from my original build) and three.cjs (this one is from this library). This is caused by the current version 1.0.7.

This fixes duplicate builds by adding a separate build for es6 in the /lib/esm directory and specifying the module entrypoint.

Details

• Also upgrades three to 0.143.0 which is what I am using (is that ok?)
• Adds a build step that outputs es6 compatible code in addition to CommonJS
• Adds the module property for the module code entrypoint /lib/esm/USDZLoader.js

[benjaminknox]

@ponahoum Thank you for this code! What do you think of this PR?

[Musadiqkhan-nullbrainer]

@benjaminknox - I am continuously getting an error. Any idea why I am getting loading USDZ model TypeError: THREE.TextureLoader is not a constructor?