Add ESM mainloop module

mainloop module

Extension of !732 (merged). This replaces imports.mainloop in modules as imports.mainloop.run() will block Promises.

The second commit enables an ESM mainloop module which exposes run() and quit(). It additionally exposes idle() as the Timers API does not cover the idle_add function (setTimeout and setInterval cover other use cases)

This example below demonstrates how run and quit can be used to start and stop the mainloop repeatedly.

import {run, quit} from 'mainloop';

setTimeout(() => {
    console.log('test 2');
    quit();
}, 1000);

console.log('test 1');

await run();

console.log('test 3');

setTimeout(() => {
    console.log('test 5');
    quit();
}, 1000); 
   
console.log('test 4');

await run();

console.log('test 6');

Another example with idle

import { run, quit, idle } from 'mainloop';

let i = 0;

setInterval(() => {
    Promise.resolve().then(() => {
        i++;

        console.log(`Count: ${i}`);

        if (i > 12) quit();
    });
}, 100);

idle(() => console.log('idle!'));

await run();

Fixes #468 (closed)