Here are some points of Rafa sliding on
HC's with both his FH and BH. Not to Djokovic levels, but still sliding:
He is sliding out of all those shots, which is very different from sliding
into the shots the way that Djokovic is deliberately doing.
To answer the question, sliding on HC is very common these days in either direction, probably more than people think. Seems to be getting more common with the younger gen as well. But few if any do it as often, consistently and effectively as Novak indeed.
The mentioned guys like Monfils and Grigor probably come closest from the top of my mind. Guys like Zverev, Rublev, Hurkacz and Sinner can be seen doing it, but not the same frequency or level.
I'd say Chung is probably the guy out there closest to copying Djokovic movement, and he slides beautifully into splits on either side. Amazing athlete (when healthy), shame he was cursed with a body of glass and so-so strokes.