build: Update ESLint to v9 (#16639)

packages/core/eslint.config.mjs

@@ -0,0 +1,46 @@
+import { defineConfig, globalIgnores } from 'eslint/config';
+import { nodeConfig } from '@n8n/eslint-config/node';
+
+export default defineConfig(
+	nodeConfig,
+	globalIgnores(['bin/*.js', 'nodes-testing/*.ts']),
+	{
+		rules: {
+			// TODO: Lower the complexity threshold
+			complexity: ['error', 27],
+			'unicorn/filename-case': ['error', { case: 'kebabCase' }],
+
+			// TODO: Remove these
+			'no-prototype-builtins': 'warn',
+			'no-empty': 'warn',
+			'no-ex-assign': 'warn',
+			'no-useless-escape': 'warn',
+			'@typescript-eslint/no-require-imports': 'warn',
+			'@typescript-eslint/require-await': 'warn',
+			'@typescript-eslint/no-base-to-string': 'warn',
+			'@typescript-eslint/prefer-optional-chain': 'warn',
+			'@typescript-eslint/prefer-nullish-coalescing': 'warn',
+			'@typescript-eslint/no-empty-object-type': 'warn',
+			'@typescript-eslint/naming-convention': 'warn',
+			'@typescript-eslint/no-array-delete': 'warn',
+			'@typescript-eslint/no-unsafe-member-access': 'warn',
+		},
+	},
+	{
+		files: ['**/*.test.ts', '**/test/**/*.ts', '**/__test__/**/*.ts', '**/__tests__/**/*.ts'],
+		rules: {
+			// TODO: Remove these
+			'prefer-const': 'warn',
+			'import-x/no-duplicates': 'warn',
+			'import-x/no-default-export': 'warn',
+			'n8n-local-rules/no-uncaught-json-parse': 'warn',
+			'@typescript-eslint/no-unsafe-assignment': 'warn',
+			'@typescript-eslint/no-unsafe-argument': 'warn',
+			'@typescript-eslint/no-unsafe-call': 'warn',
+			'@typescript-eslint/no-unsafe-return': 'warn',
+			'@typescript-eslint/unbound-method': 'warn',
+			'@typescript-eslint/no-unused-expressions': 'warn',
+			'id-denylist': 'warn',
+		},
+	},
+);