datatypes: add a Set.array/0 method to help get all the elements from a set as an array (#24206)

vlib/datatypes/set.v

@@ -128,3 +128,8 @@ pub fn (l Set[T]) subset(r Set[T]) bool {
 	}
 	return true
 }
+
+// array returns an array representation of the set
+pub fn (l Set[T]) array() []T {
+	return l.elements.keys()
+}

vlib/datatypes/set_test.v

@@ -131,3 +131,9 @@ fn test_subset() {
 	subset.add_all(['b', 'c'])
 	assert set.subset(subset)
 }
+
+fn test_array() {
+	mut set := Set[string]{}
+	set.add_all(['a', 'b', 'c'])
+	assert set.array().len == 3
+}