What is the recommended method to shorten a formica counter top so as not to produce a chipped and jagged edge?

I would use a circular saw with a veneer cutting blade and masking tape over your line

A router with a veneer blade if you are near the edge. I do what razor recommends to get within 1/8" then use the router.

You are correct ballengerb1 the router would make the edge smooth again. Thanks for the reminder. It has been awhile

Not in your case I wouldn't think but if the counter top is not attached you can just flip it upside down and cut it, no chiping there, but if it is already attached a skill saw is what I use, but I tape it first to where the cut line is on the tape, I then score it with a knife a few time and then cut it, and finish up with a jig saw when I get close to the wall.
As for the router, if you can clamp a straight edge down to it then that would be the most accurate way to cut it.