Port to ESM w/ commonjs back-conversion

[ayjayt]

I just finished a conversion of graphlib from CJS to ESM. The source is converted, and babel is then used to recreate the original CJS so current systems don't break.

https://github.com/dagrejs/graphlib/pull/189/files

I'm planning on doing the same thing today for dagrejs, and making my way all the way up to cytoscape.

I understand this is a large set of changes.

I understand if the changes don't make it into the main repo, I will end up with a fork which I will maintain to the best of my ability.

Thank you!