What was the first version of macOS to ship with the Vim text editor? Since macOS (originally Mac OS X) is a variant of UNIX, and has been POSIX-certified for a while, I assume it’s always had the vi text editor available. In recent versions, it has come with Vim. Has the system always shipped with Vim specifically, or was there a time when macOS shipped with a different variant of vi?

This capture by the Wayback Machine shows that Vim has been included at least as far back as Mac OS X 10.6.6. Unfortunately, Apple seems to have deleted a lot of old documentation (or at least broken all of the links) so I’m not sure whether you can get older OS versions’ man pages online in this same way.
vim has been included with OS X since version 10.3.0 (Panther); vi has been included from the very first version, 10.0 (Cheetah).

Apple has an excellent Open Source repository - http://opensource.apple.com - where they keep an archive of all the software that they've used in the development of their operating systems.  Looking at details of the 10.3 Project, you will see that vim made its first appearance.