fix(status_codes): update HTTP status constants to conform to RFC 9110

[alexandrubunea]

Summary of Changes

Updated HTTP status code constants accordingly to RFC 9110. The following status codes have been updated:

• 413 Payload Too Large => 413 Content Too Large
• 422 Unprocessable Entity => 422 Unprocessable Content

Related Issues

2276

Pull Request Checklist (edited by @vytas7)

• [x] Update all constants per RFC 9110.
• [ ] Add new HTTP error classes, e.g., HTTPContentTooLarge.
• [ ] Mark the old HTTP error classes as deprecated.
• [ ] Alias the old HTTP symbolic constants in addition to the new ones, but don't export them via __all__ nor falcon.__all__.
• [ ] Add a Towncrier newsfragment.
• [ ] Update status definitions in docs/api/status.rst.