New Issue: Retire 'set.isIntersecting()' method

18644, "bmcdonald3", "Retire 'set.isIntersecting()' method", "2021-10-28T20:03:43Z"

The same behavior of set.isIntersecting() can be achieved through !set.isDisjoint(), so the extra method seems extraneous. Additionally, there isn't much of a precedence for this method in other languages, and the ing naming is something that is fairly unique to this method in the Chapel codebase.