Use tsc to compile a cjs module and export that, rather than esm.

[aboodman]

It's easy enough to generate both, but after reading https://redfin.engineering/node-modules-at-war-why-commonjs-and-es-modules-cant-get-along-9617135eeca1, it just doesn't seem that valuable and creates extra crap to test and maintain, as well as potential problems.