replace .eslintrc.json with eslint.config.mjs (preferred for next 15)

Author: mathu97

starters/nextjs/basic/.eslintrc.json

@@ -0,0 +1,11 @@
+import { FlatCompat } from "@eslint/eslintrc";
+const compat = new FlatCompat({
+  // import.meta.dirname is available after Node.js v20.11.0
+  baseDirectory: import.meta.dirname,
+});
+const eslintConfig = [
+  ...compat.config({
+    extends: ["next/core-web-vitals"],
+  }),
+];
+export default eslintConfig;