Devtools: Fix build-for-devtools (#28976)

Author: eps1lon

package.json

@@ -108,7 +108,7 @@
   },
   "scripts": {
     "build": "node ./scripts/rollup/build-all-release-channels.js",
-    "build-for-devtools": "cross-env RELEASE_CHANNEL=experimental yarn build react/index,react/jsx,react-dom/index,react-dom/unstable_testing,react-dom/test-utils,react-is,react-debug-tools,scheduler,react-test-renderer,react-refresh,react-art --type=NODE",
+    "build-for-devtools": "cross-env RELEASE_CHANNEL=experimental yarn build react/index,react/jsx,react-dom/index,react-dom/client,react-dom/unstable_testing,react-dom/test-utils,react-is,react-debug-tools,scheduler,react-test-renderer,react-refresh,react-art --type=NODE",
     "build-for-devtools-dev": "yarn build-for-devtools --type=NODE_DEV",
     "build-for-devtools-prod": "yarn build-for-devtools --type=NODE_PROD",
     "linc": "node ./scripts/tasks/linc.js",

packages/react-devtools-extensions/webpack.backend.js

@@ -75,6 +75,8 @@ module.exports = {
       __DEV__: true,
       __PROFILE__: false,
       __DEV____DEV__: true,
+      // By importing `shared/` we may import ReactFeatureFlags
+      __EXPERIMENTAL__: true,
       'process.env.DEVTOOLS_PACKAGE': `"react-devtools-extensions"`,
       'process.env.DEVTOOLS_VERSION': `"${DEVTOOLS_VERSION}"`,
       'process.env.GITHUB_URL': `"${GITHUB_URL}"`,