Google Docs actually has this and hides it behind terrible UI/UX. You can "Name this version" of a doc, and there's a separate page to view versions (from which you can name versions as well).

The diffing isn't there, or at least not to the degree that code review tools offer.

I'm not sure the feature has evolved in years either. Definitely feels like one of those things a Google engineer threw into production one day, and it's never been considered again.