doc: update mailmap and AUTHORS

Based on their GitHub and other social media profiles as well as the
most recent of their authored commits, I suspect watson goes by "Thomas
Watson" and not the name currently listed in the .mailmap and AUTHORS
files. Update.

I'm doing this because it  helps avoid false positives in
`find-inactive-collaborators.mjs` which uses `git shortlog` which uses
`.mailmap`.

PR-URL: https://github.com/nodejs/node/pull/39393


Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>