Bump frontend_server_client from 3.2.0 to 4.0.0 in /build_runner

Bumps [frontend_server_client](https://github.com/dart-lang/webdev) from 3.2.0 to 4.0.0.
- [Release notes](https://github.com/dart-lang/webdev/releases)
- [Commits](https://github.com/dart-lang/webdev/commits)

---
updated-dependencies:
- dependency-name: frontend_server_client
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

build_runner/pubspec.yaml

@@ -24,7 +24,7 @@ dependencies:
   collection: ^1.15.0
   crypto: ^3.0.0
   dart_style: ^2.0.0
-  frontend_server_client: ^3.0.0
+  frontend_server_client: ^4.0.0
   glob: ^2.0.0
   graphs: ^2.2.0
   http_multi_server: ^3.0.0