Migrate to ESLint flat config (microsoft#1784)

* Migrate to ESLint flat config

* Updates from editor

Fix package-lock.json by installing 8.3.0 and copying result over.

---------

Co-authored-by: Nathan Shively-Sanders <293473+sandersn@users.noreply.github.com>

Author: MattiasBuelens

eslint.config.mjs

@@ -1,37 +1,20 @@
-import typescriptEslint from "@typescript-eslint/eslint-plugin";
+// @ts-check
+
+import typescriptEslint from "typescript-eslint";
 import globals from "globals";
-import tsParser from "@typescript-eslint/parser";
-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,
-});
+import prettierRecommended from "eslint-plugin-prettier/recommended";
 
-export default [
-  ...compat.extends(
-    "eslint:recommended",
-    "plugin:@typescript-eslint/recommended",
-    "plugin:prettier/recommended",
-  ),
+export default typescriptEslint.config(
+  js.configs.recommended,
+  ...typescriptEslint.configs.recommended,
+  prettierRecommended,
   {
-    plugins: {
-      "@typescript-eslint": typescriptEslint,
-    },
-
     languageOptions: {
       globals: {
         ...globals.node,
         ...globals.browser,
       },
-
-      parser: tsParser,
     },
 
     rules: {
@@ -41,4 +24,4 @@ export default [
       "@typescript-eslint/no-var-requires": 0,
     },
   },
-];
+);

package-lock.json

@@ -37,6 +37,7 @@
   "license": "Apache-2.0",
   "type": "module",
   "devDependencies": {
+    "@eslint/js": "^9",
     "@mdn/browser-compat-data": "^5.5.21",
     "@octokit/rest": "^21.0.0",
     "@types/node": "^22.2.0",
@@ -54,11 +55,13 @@
     "eslint": "^9.9.0",
     "eslint-config-prettier": "^9.1.0",
     "eslint-plugin-prettier": "^5.1.3",
+    "globals": "^15.9.0",
     "jsonc-parser": "^3.2.1",
     "node-fetch": "^3.3.2",
     "prettier": "^3.2.5",
     "print-diff": "^2.0.0",
     "typescript": "^5.6.0-dev.20240806",
+    "typescript-eslint": "^8",
     "webidl2": "^24.4.1"
   },
   "overrides": {