Fix spurious parse error for rational real array constants (#3554)

Fix spurious parse error for rational real array constants (#3554)

Currently we can't parse constant arrays that store real values that are given as rationals `(/ n m)`. We throw a spurious parse error for `((as const (Array Int Real)) (/ 1 3))`, indicating that the argument of the array is not constant. This is caused by the fact that `(/ 1 3)` is parsed as a *division* term not a rational value.

This adds a special case to constant array construction so that we compute the result of a constant division instead of using the division term `(/ n m)` when constructing an array constant.