Fix up ESLint flat config resolution (replace #1173)

Author: webpro

packages/knip/fixtures/plugins/eslint5/eslint.config.ts

@@ -0,0 +1,21 @@
+import js from '@eslint/js';
+import { importX } from 'eslint-plugin-import-x';
+import tsParser from '@typescript-eslint/parser';
+
+export default [
+  js.configs.recommended,
+  importX.flatConfigs.recommended,
+  importX.flatConfigs.typescript,
+  {
+    files: ['**/*.{js,mjs,cjs,jsx,mjsx,ts,tsx,mtsx}'],
+    languageOptions: {
+      parser: tsParser,
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+    },
+    rules: {
+      'import-x/no-dynamic-require': 'warn',
+      'import-x/no-nodejs-modules': 'warn',
+    },
+  },
+];

packages/knip/fixtures/plugins/eslint5/knip.json

@@ -0,0 +1,3 @@
+{
+  "eslint": ["eslint.config.ts"]
+}