Support Node16 ESM resolution

[cometkim]

This is re-trying PR from #137

Tested on Node v16 with TypeScript v3.8, both CommonJS and ESM

node index.mjs test: OK

import {Command, Option, runExit} from 'clipanion';
 
runExit(class MainCommand extends Command {
  name = Option.String();
 
  async execute() {
    this.context.stdout.write(`Hello ${this.name}!\n`);
  }
})

node index.cjs test OK

const {Command, Option, runExit} = require('clipanion');
 
runExit(class MainCommand extends Command {
  name = Option.String();
 
  async execute() {
    this.context.stdout.write(`Hello ${this.name}!\n`);
  }
})

Note this PR will drop support for Node v14

[cometkim]

Also it should closes #113

[cometkim]

mocha's ESM Resolver doesn't seem to respect exports correctly
It does, but it doesn't correctly resolve source in TypeScript

[cometkim]

Note: multi-input bundle output is broken on rollup@v3

[cometkim]

Any chance of getting merged? maybe it should be the next major?

[niieani]

Looks good! Would also help with #147.

[cometkim]

@arcanis cleaned up to be minimal changeset to support NodeJS/TypeScript ESM

[merceyz]

It's not supposed to be exposed to consumers and bundlers should follow the browser field if needed.

[cometkim]

The browser field exists for some legacy bundlers and is not supported by the whole ecosystem widely. eg. TypeScript

[merceyz]

This change shouldn't be needed.

[cometkim]

This is the node's native way, compatible with the whole ecosystem, including Node, TS, and modern bundlers

[merceyz]

Rollup includes its own types.

[cometkim]

It's rollup v2

[cometkim]

I added e2e.test.ts for ensure Node ESM import and TypeScript configuration work, which is failed without those changes. I tried to make as few changes as possible to fix it.

This is currently the only configuration that is compatible with node, tsc, and @rollup/plugin-node-resolve.