Use ESLint Flat Config (#84800)

Author: eps1lon

.config/eslintignore.mjs

@@ -0,0 +1,58 @@
+import { globalIgnores } from 'eslint/config'
+
+export default globalIgnores([
+  '**/.*/**/*', // Default of ESLint legacy config
+  '**/node_modules',
+  '**/.next/**/*',
+  '**/_next/**/*',
+  '**/.vscode/**/*',
+  '**/dist/**/*',
+  'e2e-tests/**/*',
+  'examples/cms-sanity/sanity.types.ts',
+  'examples/with-eslint/**/*',
+  'examples/with-typescript-eslint-jest/**/*',
+  'examples/with-kea/**/*',
+  'examples/with-custom-babel-config/**/*',
+  'examples/with-flow/**/*',
+  'examples/with-jest/**/*',
+  'examples/with-mobx-state-tree/**/*',
+  'examples/with-mobx/**/*',
+  'examples/with-tigris/db/models/todoItems.ts',
+  'packages/next/src/bundles/webpack/packages/*.runtime.js',
+  'packages/next/src/bundles/webpack/packages/lazy-compilation-*.js',
+  'packages/next/src/compiled/**/*',
+  'packages/next/wasm/@next',
+  'packages/react-refresh-utils/**/*.js',
+  'packages/react-dev-overlay/lib/**/*',
+  '**/__tmp__/**/*',
+  '.github/actions/next-stats-action/.work',
+  'packages/next-codemod/transforms/__testfixtures__/**/*',
+  'packages/next-codemod/transforms/__tests__/**/*',
+  'packages/next-codemod/bin/__testfixtures__/**/*',
+  'packages/next-codemod/**/*.js',
+  'packages/next-codemod/**/*.d.ts',
+  'packages/next-env/**/*.d.ts',
+  'packages/create-next-app/templates/**/*',
+  'test/integration/eslint/**/*.js',
+  'test/integration/script-loader/**/*.js',
+  'test/development/basic/legacy-decorators/**/*.js',
+  'test/production/emit-decorator-metadata/**/*.js',
+  '!test/**/*.test.*',
+  'test/e2e/app-dir/rsc-errors/app/swc/use-client/page.js',
+  '**/test-timings.json',
+  'crates/**/*',
+  'bench/nested-deps/**/*',
+  'bench/nested-deps-app-router/**/*',
+  'bench/heavy-npm-deps/**/*',
+  'packages/next-bundle-analyzer/index.d.ts',
+  'examples/with-typescript-graphql/lib/gql/',
+  'test/development/basic/hmr/components/parse-error.js',
+  'test/development/mcp-server/fixtures/default-template/app/build-error/page.tsx',
+  'packages/next-swc/docs/assets/**/*',
+  'test/e2e/app-dir/server-source-maps/fixtures/default/internal-pkg/sourcemapped.js',
+  'test/e2e/app-dir/server-source-maps/fixtures/default/external-pkg/sourcemapped.js',
+  'test/development/next-lint-eslint-formatter-compact/**/*.js',
+  'test/e2e/app-dir/app-external/app/mixed/import/mixed-mod.mjs',
+  'turbopack/crates/*/tests/**/*',
+  'turbopack/crates/*/js/src/compiled',
+])