Get comment author from the comment user_id field

[goldenapples]

Updates the get_comment_author function to retrieve the comment author ID from the "user_id" field of the comment rather than assuming the current user is the author of the comment.

Fixes #1428.

Describe your approach and how it fixes the issue.

Checklist

• Project documentation has been updated to reflect the changes in this pull request, if applicable.
• I have tested the changes in the local development environment (see contributing.md).
• I have added phpunit tests.

Release Changelog

• Fix: Updates the get_comment_author function to show the comment author rather than the current user.

Release Checklist

• This pull request is to the master branch.
• Release version follows semantic versioning. Does it include breaking changes?
• Update changelog in readme.txt.
• Bump version in stream.php.
• Bump Stable tag in readme.txt.
• Bump version in classes/class-plugin.php.
• Draft a release on GitHub.

Change [ ] to [x] to mark the items as done.

[kasparsd]

This is great, thank you!