CLJS-1809: Add 0/1 arity to into

Author: anmonteiro

src/main/cljs/cljs/core.cljs

@@ -4762,6 +4762,8 @@ reduces them without incurring seq initialization"
 (defn into
   "Returns a new coll consisting of to-coll with all of the items of
   from-coll conjoined. A transducer may be supplied."
+  ([] [])
+  ([to] to)
   ([to from]
      (if-not (nil? to)
        (if (implements? IEditableCollection to)

src/test/cljs/cljs/collections_test.cljs

@@ -611,3 +611,7 @@
     (is (= (get m 1) 2))
     (is (= (get m 3) 4))
     (is (= m {1 2 3 4}))))
+
+(deftest test-cljs-1809
+  (is (= (into) []))
+  (is (= (into [1 2]) [1 2])))