Switch from CommonJS to ESM modules

[Balearica]

This would be one way of fixing #876, and should probably happen eventually regardless.

[laurent22]

Please don't switch to ESM or keep the CommonJS release too. Many projects cannot easily switch to ESM and TesseractJS is unique enough that it won't be possible to find an alternative for non-ESM projects.

[Balearica]

I've removed the v6 milestone. My understanding is that the Node.js ecosystem will transition to ESM eventually, however I don't think we need to be on the bleeding edge of this, and most Node.js projects are still using CJS. Looking at node-fetch (the reason this came up), just 5 million of the 43 million weekly downloads (12%) are from the ESM versions.

[laurent22]

Thank you for taking the time to investigate this.