ESM all the things

This PR changes all internal code (scripts/, test/, util/) to ESM. The
built package for NPM now contains an ESM and CJS entrypoint.

README.md

@@ -25,7 +25,7 @@ npm install @mdn/browser-compat-data
 ## Usage
 
 ```js
-const bcd = require('@mdn/browser-compat-data');
+import bcd from '@mdn/browser-compat-data';
 bcd.css.properties.background;
 // returns a compat data object (see schema)
 ```

index.d.ts

@@ -1,9 +1,6 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
-/// <reference path="./types.d.ts"/>
+
 import { CompatData } from './types';
 
-// This is necessary to have intellisense in projects which
-// import data from this package.
-declare const compatData: CompatData;
-export = compatData;
+export default CompatData;

index.js

@@ -1,6 +1,8 @@
-'use strict';
-const fs = require('fs');
-const path = require('path');
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const dirname = fileURLToPath(new URL('.', import.meta.url));
 
 function load() {
   // Recursively load one or more directories passed as arguments.
@@ -32,7 +34,7 @@ function load() {
   }
 
   for (dir of arguments) {
-    dir = path.resolve(__dirname, dir);
+    dir = path.resolve(dirname, dir);
     fs.readdirSync(dir).forEach(processFilename);
   }
 
@@ -59,7 +61,7 @@ function extend(target, source) {
   }
 }
 
-module.exports = load(
+export default load(
   'api',
   'browsers',
   'css',