How to retrieve the reviewer list of a PR as shown on the webpage from API

[Keyi Ni]

The `reviewers` entry in the response of

/2.0/repositories/{username}/{repo_slug}/pullrequests/{pull_request_id}

is different from the list of reviewers in a PR's webpage. What happens is in the API response, a user appears to be a reviewer on the web page can have a role of participant and falls into the `participants` entry. Is there a way to retrieve the same list of reviewer as the one shown on the web page via API?