Initial conversion to ESM module

[lyricnz]

Per #361

TLDR:

• append .js to all local imports
• use node:fs not fs
• a couple of require -> import for dynamic imports; add .js suffix
• kludge to emulate __dirname
• rename/update webpack config
• change type etc in package.json
• fix? webpack step ordering

Then:

• Update to chai@5 and chai-as-promised@8
• Update all other modules

[lyricnz]

@alutman-innablr @abukharov

[lyricnz]

• build works

• tests work

• lint works

• bundle works

• coverage (nyc) does not work - changed to c8 https://github.com/bcoe/c8