Make ES module compatible with node core ESM loader

[pravi]

As discussed with nodejs maintainers here -> nodejs/help#2081 (comment) node core esm loader does not recognise "module" field.

As per https://nodejs.org/api/esm.html#esm_package_entry_points I think you need to provide a .mjs file as ES module entry point or add "type": " module" and provide commonjs entry point as .cjs file. I hope one of these options can be considered to make it work with node core ESM loader.