Skip default logging for client errors

[raashish1601]

Summary

Avoid logging errors from the default final handler when the resolved response status is a client error (4xx). Server errors continue to be logged in non-test environments.

Why

Express currently logs any error object that reaches the default final handler. For expected client errors such as 404 or 400, this adds noisy console.error output even though the response is already a client-error response.

Fixes #2263.

Testing

• npx mocha --require test/support/env --reporter spec --check-leaks test/app.js
• npx eslint lib/application.js test/app.js
• npm test
• npm run lint

[krzysdz]

As stated in #2263 (comment), Express should not duplicate the logic from finalhandler and instead the status determined by finalhandler should be passed to the error handler to decide whether a message should be logged.