Bundle to esm and cjs

[steveruizok]

This PR changes the build process so that the library outputs a format in both commonjs and esmodules.

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[tomayac]

@steveruizok In order to land this, could I ask you to make the bot 🤖 happy?

[steveruizok]

Done! (I think)

[tomayac]

@steveruizok, once you have done the work the bot asks you to do, you need to respond here with "@googlebot I signed it!". (Sorry for the hassle.)

[tomayac]

Oh, looks like as long as anyone responds with the magic phrase the bot is happy (if you have signed the thing). So ignore. Thank you!