Update JavaScript codebase to use ESM module

Dropped support for Node.js 16, 18.
Updated ESLint to v9 since assert is not supported in v8. See:
eslint/eslint#15305

Dropping support for Node v16, v18 should be fine as they are both EOL.

Consequently had to drop support for Wikimedia/eslint rules as it
doesn't yet support ESLint v9.

Bug: https://phabricator.wikimedia.org/T407180
Change-Id: I44dee29b49804da5a13d986352148931baf7cb34

Author: Abijeet

.eslintrc.json

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-v: [16.x, 18.x, 20.x]
+        node-v: [20.x, 22.x, 24.x]
     steps:
       - name: Checkout
         uses: actions/checkout@v4

.github/workflows/node.yml

@@ -78,10 +78,10 @@ The basic usage is like this:
 
 .. code-block:: js
 
-		const languageData = require('@wikimedia/language-data');
+		import { getAutonym } from '@wikimedia/language-data';
 
 		// Returns English
-		languageData.getAutonym( 'en');
+		getAutonym( 'en');
 
 The exposed methods are similar to the methods present in the PHP `LanguageUtil <api/languagedata/languageutil.html>`_ class.
 

docs/index.rst

@@ -0,0 +1,25 @@
+import { defineConfig } from "eslint/config";
+import globals from "globals";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import js from "@eslint/js";
+import { FlatCompat } from "@eslint/eslintrc";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const compat = new FlatCompat({
+    baseDirectory: __dirname,
+    recommendedConfig: js.configs.recommended,
+    allConfig: js.configs.all
+});
+
+export default defineConfig([{
+    languageOptions: {
+        globals: {
+            ...globals.browser,
+            ...globals.node,
+            ...globals.mocha,
+            require: false,
+        },
+    },
+}]);