[FEATURE] Remove duplicate empty set representations in arrays encoding

[rodrigo7491]

In the initial version of the arrays encoding, every set declaration is followed by an equality to a new empty set, as shown below.

(declare-const set1 (Array some_sort Bool))
(assert (= set1 ((as const (Array some_sort Bool)) false)))

As suggested by Nikolaj Bjorner in an e-mail exchange, we should define constant empty sets for every type used in the spec and refer to them instead, as shown below for integers.

(define-const emptyIntSet (Array Int Bool) ((as const (Array Int Bool)) false))
(declare-const set1 (Array Int Bool))
(assert (= set1 emptyIntSet))